perf stat: Merge uncore events by default for hybrid platform

On a hybrid platform, by default 'perf stat' aggregates and reports the
event counts per PMU. For example,

  # perf stat -e cycles -a true

   Performance counter stats for 'system wide':

           1,400,445      cpu_core/cycles/
             680,881      cpu_atom/cycles/

         0.001770773 seconds time elapsed

But for uncore events that's not a suitable method. Uncore has nothing
to do with hybrid. So for uncore events, we aggregate event counts from
all PMUs and report the counts without PMUs.

Before:

  # perf stat -e arb/event=0x81,umask=0x1/,arb/event=0x84,umask=0x1/ -a true

   Performance counter stats for 'system wide':

               2,058      uncore_arb_0/event=0x81,umask=0x1/
               2,028      uncore_arb_1/event=0x81,umask=0x1/
                   0      uncore_arb_0/event=0x84,umask=0x1/
                   0      uncore_arb_1/event=0x84,umask=0x1/

         0.000614498 seconds time elapsed

After:

  # perf stat -e arb/event=0x81,umask=0x1/,arb/event=0x84,umask=0x1/ -a true

   Performance counter stats for 'system wide':

               3,996      arb/event=0x81,umask=0x1/
                   0      arb/event=0x84,umask=0x1/

         0.000630046 seconds time elapsed

Of course, we also keep the '--no-merge' working for uncore events.

  # perf stat -e arb/event=0x81,umask=0x1/,arb/event=0x84,umask=0x1/ --no-merge true

   Performance counter stats for 'system wide':

               1,952      uncore_arb_0/event=0x81,umask=0x1/
               1,921      uncore_arb_1/event=0x81,umask=0x1/
                   0      uncore_arb_0/event=0x84,umask=0x1/
                   0      uncore_arb_1/event=0x84,umask=0x1/

         0.000575536 seconds time elapsed

Signed-off-by: Jin Yao <yao.jin@linux.intel.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Kan Liang <kan.liang@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210707055652.962-1-yao.jin@linux.intel.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>