Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/arch/mips/Kbuild b/arch/mips/Kbuild
index 5cef586..a8d5e4f 100644
--- a/arch/mips/Kbuild
+++ b/arch/mips/Kbuild
@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: GPL-2.0
 # Fail on warnings - also for files referenced in subdirs
 # -Werror can be disabled for specific files using:
 # CFLAGS_<file.o> := -Wno-error