perf stat aggregation: Add separate socket member

Add socket as a separate member so that it doesn't have to be packed
into the int value.

When the socket ID was larger than 8 bits the output appeared corrupted
or incomplete.

For example, here on ThunderX2 'perf stat' reports a socket of -1 and an
invalid die number:

  ./perf stat -a --per-die
  The socket id number is too big.

  Performance counter stats for 'system wide':

  S-1-D255       128             687.99 msec cpu-clock                 #   57.240 CPUs utilized
  ...
  S36-D0         128             842.34 msec cpu-clock                 #   70.081 CPUs utilized
  ...

And with --per-core there is an entry with an invalid core ID:

  ./perf stat record -a --per-core
  The socket id number is too big.

  Performance counter stats for 'system wide':
  S-1-D255-C65535     128             671.04 msec cpu-clock                 #   54.112 CPUs utilized
  ...
  S36-D0-C0           4              28.27 msec cpu-clock                 #    2.279 CPUs utilized
  ...

This fixes the "Session topology" self test on ThunderX2.

After this fix the output contains the correct socket and die IDs and no
longer prints a warning about the size of the socket ID:

  ./perf stat --per-die -a

  Performance counter stats for 'system wide':

  S36-D0         128         169,869.39 msec cpu-clock                 #  127.501 CPUs utilized
  ...
  S3612-D0         128         169,733.05 msec cpu-clock                 #  127.398 CPUs utilized

Signed-off-by: James Clark <james.clark@arm.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Tested-by: John Garry <john.garry@huawei.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Richter <tmricht@linux.ibm.com>
Link: https://lore.kernel.org/r/20201126141328.6509-10-james.clark@arm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>