perf tools: Add signal.h to places using its definitions

And remove it from util.h, disentangling it a bit more.

Link: http://lkml.kernel.org/n/tip-2zg9s5nx90yde64j3g4z2uhk@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
index f74ea2e..8d36cf3 100644
--- a/tools/perf/util/evlist.c
+++ b/tools/perf/util/evlist.c
@@ -18,6 +18,7 @@
 #include "evsel.h"
 #include "debug.h"
 #include "asm/bug.h"
+#include <signal.h>
 #include <unistd.h>
 
 #include "parse-events.h"