perf tools: Move event prototypes from util.h to event.h

More needs to be done to have the actual functions and variables in a
smaller .c file that can then be included in the python binding,
avoiding dragging more stuff into it.

Link: http://lkml.kernel.org/n/tip-uecxz7cqkssouj7tlxrkqpl4@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/tests/hists_output.c

@@ -1,5 +1,6 @@
 #include "perf.h"
 #include "util/debug.h"
+#include "util/event.h"
 #include "util/symbol.h"
 #include "util/sort.h"
 #include "util/evsel.h"