perf hist: Basic support for mem_stat accounting

Add a logic to account he->mem_stat based on mem_stat_type in hists.

Each mem_stat entry will have different meaning based on the type so the
index in the array is calculated at runtime using the corresponding
value in the sample.data_src.

Still hists has no mem_stat_types yet so this code won't work for now.

Later hists->mem_stat_types will be allocated based on what users want
in the output actually.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
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/20250430205548.789750-6-namhyung@kernel.org


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