perf stat: Support 'percore' event qualifier

With this patch, we can use the 'percore' event qualifier in perf-stat.

  root@skl:/tmp# perf stat -e cpu/event=0,umask=0x3,percore=1/,cpu/event=0,umask=0x3/ -a -A -I1000
    1.000773050 S0-C0   98,352,832 cpu/event=0,umask=0x3,percore=1/  (50.01%)
    1.000773050 S0-C1  103,763,057 cpu/event=0,umask=0x3,percore=1/  (50.02%)
    1.000773050 S0-C2  196,776,995 cpu/event=0,umask=0x3,percore=1/  (50.02%)
    1.000773050 S0-C3  176,493,779 cpu/event=0,umask=0x3,percore=1/  (50.02%)
    1.000773050 CPU0    47,699,641 cpu/event=0,umask=0x3/            (50.02%)
    1.000773050 CPU1    49,052,451 cpu/event=0,umask=0x3/            (49.98%)
    1.000773050 CPU2   102,771,422 cpu/event=0,umask=0x3/            (49.98%)
    1.000773050 CPU3   100,784,662 cpu/event=0,umask=0x3/            (49.98%)
    1.000773050 CPU4    43,171,342 cpu/event=0,umask=0x3/            (49.98%)
    1.000773050 CPU5    54,152,158 cpu/event=0,umask=0x3/            (49.98%)
    1.000773050 CPU6    93,618,410 cpu/event=0,umask=0x3/            (49.98%)
    1.000773050 CPU7    74,477,589 cpu/event=0,umask=0x3/            (49.99%)

In this example, we count the event 'ref-cycles' per-core and per-CPU in
one perf stat command-line. From the output, we can see:

  S0-C0 = CPU0 + CPU4
  S0-C1 = CPU1 + CPU5
  S0-C2 = CPU2 + CPU6
  S0-C3 = CPU3 + CPU7

So the result is expected (tiny difference is ignored).

Note that, the 'percore' event qualifier needs to use with option '-A'.

Signed-off-by: Jin Yao <yao.jin@linux.intel.com>
Tested-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jin Yao <yao.jin@intel.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1555077590-27664-4-git-send-email-yao.jin@linux.intel.com


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