perf stat: Merge event counts from all hybrid PMUs

perf stat: Merge event counts from all hybrid PMUs

For hybrid events, by default stat aggregates and reports the event counts
per pmu.

  # ./perf stat -e cycles -a  sleep 1

   Performance counter stats for 'system wide':

      14,066,877,268      cpu_core/cycles/
       6,814,443,147      cpu_atom/cycles/

         1.002760625 seconds time elapsed

Sometimes, it's also useful to aggregate event counts from all PMUs.
Create a new option '--hybrid-merge' to enable that behavior and report
the counts without PMUs.

  # ./perf stat -e cycles -a --hybrid-merge  sleep 1

   Performance counter stats for 'system wide':

      20,732,982,512      cycles

         1.002776793 seconds time elapsed

Reviewed-by: Kan Liang <kan.liang@linux.intel.com>
Signed-off-by: Xing Zhengjun <zhengjun.xing@linux.intel.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220422065635.767648-2-zhengjun.xing@linux.intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>