perf tools: Add include <linux/kernel.h> where ARRAY_SIZE() is used

To pave the way for further cleanups where linux/kernel.h may stop being
included in some header.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-qqxan6tfsl6qx3l0v3nwgjvk@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c
index 4d7e65f..a0f59f6 100644
--- a/tools/perf/util/event.c
+++ b/tools/perf/util/event.c
@@ -1,3 +1,4 @@
+#include <linux/kernel.h>
 #include <linux/types.h>
 #include <uapi/linux/mman.h> /* To get things like MAP_HUGETLB even on older libc headers */
 #include <api/fs/fs.h>