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>

tools/perf/builtin-kvm.c

@@ -31,6 +31,7 @@
 #include <inttypes.h>
 #include <termios.h>
 #include <semaphore.h>
+#include <signal.h>
 #include <pthread.h>
 #include <math.h>