perf: Clean up perf ctx time

perf: Clean up perf ctx time

The current perf tracks two timestamps for the normal ctx and cgroup.
The same type of variables and similar codes are used to track the
timestamps. In the following patch, the third timestamp to track the
guest time will be introduced.
To avoid the code duplication, add a new struct perf_time_ctx and factor
out a generic function update_perf_time_ctx().

No functional change.

Suggested-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
Signed-off-by: Mingwei Zhang <mizhang@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Xudong Hao <xudong.hao@intel.com>
Link: https://patch.msgid.link/20251206001720.468579-6-seanjc@google.com