perf tools: Move event synthesizing routines to separate header

Those are the only routines using the perf_event__handler_t typedef and
are all related, so move to a separate header to reduce the header
dependency tree, lots of places were getting event.h and even stdio.h,
limits.h indirectly, so fix those as well.

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-yvx9u1mf7baq6cu1abfhbqgs@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/tests/hists_common.c

@@ -2,6 +2,7 @@
 #include <inttypes.h>
 #include "util/debug.h"
 #include "util/dso.h"
+#include "util/event.h" // struct perf_sample
 #include "util/map.h"
 #include "util/symbol.h"
 #include "util/sort.h"
@@ -10,6 +11,7 @@
 #include "util/thread.h"
 #include "tests/hists_common.h"
 #include <linux/kernel.h>
+#include <linux/perf_event.h>
 
 static struct {
 	u32 pid;