Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/lib/Kconfig.kgdb b/lib/Kconfig.kgdb
index ab4ff0e..bbe397d 100644
--- a/lib/Kconfig.kgdb
+++ b/lib/Kconfig.kgdb
@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: GPL-2.0-only
 
 config HAVE_ARCH_KGDB
 	bool