perf mem: Add 'snoop' output field

perf mem: Add 'snoop' output field

This is a breakdown of perf_mem_data_src.mem_snoop values.  For now, it
doesn't use mem_snoopx values like FWD and PEER.

  $ perf mem report -F overhead,snoop,comm --stdio
  ...
  #           ---------- Snoop -----------
  # Overhead      Hit   HitM   Miss  Other  Command
  # ........  ............................  ...............
  #
      34.24%     0.6%   0.0%   0.0%  99.4%  gnome-shell
      12.02%     1.0%   0.0%   0.0%  99.0%  chrome
       9.32%     1.0%   0.0%   0.3%  98.7%  Isolated Web Co
       6.85%     1.0%   0.3%   0.0%  98.6%  swapper
       6.30%     0.8%   0.8%   0.0%  98.5%  Xorg
       3.02%     2.4%   0.0%   0.0%  97.6%  VizCompositorTh
       2.35%     0.0%   0.0%   0.0% 100.0%  firefox-esr
       2.04%     0.0%   0.0%   0.0% 100.0%  JS Helper
       1.51%     3.2%   0.0%   0.0%  96.8%  threaded-ml
       1.44%     0.0%   0.0%   0.0% 100.0%  AudioIP~allback
       ...

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Leo Yan <leo.yan@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ravi Bangoria <ravi.bangoria@amd.com>
Link: https://lore.kernel.org/r/20250430205548.789750-11-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>