perf sched stats: Add support for diff subcommand

perf sched stats: Add support for diff subcommand

`perf sched stats diff` subcommand will take two perf.data files as an
input and it will print the diff between the two perf.data files. The
default input to this subcommnd is perf.data.old and perf.data.

Example usage:

 # perf sched stats diff sample1.data sample2.data
 Description
 ----------------------------------------------------------------------------------------------------
 DESC                          -> Description of the field
 COUNT                         -> Value of the field
 PCT_CHANGE                    -> Percent change with corresponding base value
 AVG_JIFFIES                   -> Avg time in jiffies between two consecutive occurrence of event
 ----------------------------------------------------------------------------------------------------

 Time elapsed (in jiffies)                                        :           1,          1
 ----------------------------------------------------------------------------------------------------
 CPU: <ALL CPUS SUMMARY>
 ----------------------------------------------------------------------------------------------------
 DESC                                                                    COUNT1      COUNT2   PCT_CHANGE    PCT_CHANGE1 PCT_CHANGE2
 ----------------------------------------------------------------------------------------------------
 yld_count                                                        :           0,          0  |     0.00% |
 array_exp                                                        :           0,          0  |     0.00% |
 sched_count                                                      :           0,          0  |     0.00% |
 sched_goidle                                                     :           0,          0  |     0.00% |  (     0.00%,      0.00% )
 ttwu_count                                                       :           0,          0  |     0.00% |
 ttwu_local                                                       :           0,          0  |     0.00% |  (     0.00%,      0.00% )
 rq_cpu_time                                                      :       32565,      33525  |     2.95% |
 run_delay                                                        :           0,        436  |     0.00% |  (     0.00%,      1.30% )
 pcount                                                           :           0,          0  |     0.00% |
 ----------------------------------------------------------------------------------------------------
 CPU: <ALL CPUS SUMMARY> | DOMAIN: SMT
 ----------------------------------------------------------------------------------------------------
 DESC                                                                    COUNT1      COUNT2   PCT_CHANGE     AVG_JIFFIES1 AVG_JIFFIES2
 ----------------------------------------- <Category busy> ------------------------------------------
 busy_lb_count                                                    :           0,          0  |     0.00% |  $        0.00,        0.00 $
 busy_lb_balanced                                                 :           0,          0  |     0.00% |  $        0.00,        0.00 $
 busy_lb_failed                                                   :           0,          0  |     0.00% |  $        0.00,        0.00 $
 busy_lb_imbalance_load                                           :           0,          0  |     0.00% |
 busy_lb_imbalance_util                                           :           0,          0  |     0.00% |
 busy_lb_imbalance_task                                           :           0,          0  |     0.00% |
 busy_lb_imbalance_misfit                                         :           0,          0  |     0.00% |
 busy_lb_gained                                                   :           0,          0  |     0.00% |
 busy_lb_hot_gained                                               :           0,          0  |     0.00% |
 busy_lb_nobusyq                                                  :           0,          0  |     0.00% |  $        0.00,        0.00 $
 busy_lb_nobusyg                                                  :           0,          0  |     0.00% |  $        0.00,        0.00 $
 *busy_lb_success_count                                           :           0,          0  |     0.00% |
 *busy_lb_avg_pulled                                              :        0.00,       0.00  |     0.00% |

 ... and so on. Output contains the diff of aggregated data of all the
busy, idle and newidle categories for all the sched domains in the system.

Signed-off-by: Ravi Bangoria <ravi.bangoria@amd.com>
Signed-off-by: Swapnil Sapkal <swapnil.sapkal@amd.com>
Tested-by: Chen Yu <yu.c.chen@intel.com>
Acked-by: Ian Rogers <irogers@google.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Anubhav Shelat <ashelat@redhat.com>
Cc: Ben Gainey <ben.gainey@arm.com>
Cc: Blake Jones <blakejones@google.com>
Cc: Chun-Tse Shao <ctshao@google.com>
Cc: David Vernet <void@manifault.com>
Cc: Dmitriy Vyukov <dvyukov@google.com>
Cc: Dr. David Alan Gilbert <linux@treblig.org>
Cc: Gautham Shenoy <gautham.shenoy@amd.com>
Cc: Graham Woodward <graham.woodward@arm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@arm.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: K Prateek Nayak <kprateek.nayak@amd.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Leo Yan <leo.yan@arm.com>
Cc: Madadi Vineeth Reddy <vineethr@linux.ibm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Sandipan Das <sandipan.das@amd.com>
Cc: Santosh Shukla <santosh.shukla@amd.com>
Cc: Shrikanth Hegde <sshegde@linux.ibm.com>
Cc: Steven Rostedt (VMware) <rostedt@goodmis.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Thomas Falcon <thomas.falcon@intel.com>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Yang Jihong <yangjihong@bytedance.com>
Cc: Yujie Liu <yujie.liu@intel.com>
Cc: Zhongqiu Han <quic_zhonhan@quicinc.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>