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/ui/stdio/hist.c

@@ -5,6 +5,7 @@
 
 #include "../../util/callchain.h"
 #include "../../util/debug.h"
+#include "../../util/event.h"
 #include "../../util/hist.h"
 #include "../../util/map.h"
 #include "../../util/map_groups.h"