perf tools: Move 'struct events_stats' and prototypes to separate header

This will allow us to untangle the header dependency a bit more, as some
places will not need event.h anymore.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lkml.kernel.org/n/tip-enqncj29ovzaat3cd9203rwl@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/evlist.h

@@ -9,7 +9,7 @@
 #include <api/fd/array.h>
 #include <stdio.h>
 #include <internal/evlist.h>
-#include "event.h"
+#include "events_stats.h"
 #include "evsel.h"
 #include "mmap.h"
 #include <signal.h>