Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/arch/hexagon/Kconfig.debug b/arch/hexagon/Kconfig.debug
index 22a162c..295942f 100644
--- a/arch/hexagon/Kconfig.debug
+++ b/arch/hexagon/Kconfig.debug
@@ -1 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-only
 # dummy file, do not delete