perf hists: Split hists_stats from events_stats

Each struct hists have events_stats but most of the fields were not
used.  It's to count number of samples and periods whether filtered or
not.  And other fields are used only by evlist.

So it'd be better to split hists_stats and events_stats to reduce
wasted memory in the struct hists.  This makes the output of event
statistics in the perf report compact by skipping 0 events in each
evsel/hists.

Reviewed-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210427013717.1651674-3-namhyung@kernel.org


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