Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/arch/arm64/Kconfig.debug b/arch/arm64/Kconfig.debug
index 69c9170..cf09010 100644
--- a/arch/arm64/Kconfig.debug
+++ b/arch/arm64/Kconfig.debug
@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: GPL-2.0-only
 
 config ARM64_PTDUMP_CORE
 	def_bool n