Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/tools/perf/tests/mem.c b/tools/perf/tests/mem.c
index 0f82ee9..673a11a 100644
--- a/tools/perf/tests/mem.c
+++ b/tools/perf/tests/mem.c
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "util/map_symbol.h"
 #include "util/mem-events.h"
 #include "util/symbol.h"
 #include "linux/perf_event.h"