perf ui progress: Per progress bar state

perf ui progress: Per progress bar state

That will ease using a progress bar across multiple functions, like in
the upcoming patches that will present a progress bar when collapsing
histograms.

Based on a previous patch by Namhyung Kim.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-cr7lq7ud9fj21bg7wvq27w1u@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>