Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/arch/openrisc/mm/Makefile b/arch/openrisc/mm/Makefile
index a31b2a4..8a0e580 100644
--- a/arch/openrisc/mm/Makefile
+++ b/arch/openrisc/mm/Makefile
@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: GPL-2.0-only
 #
 # Makefile for the linux openrisc-specific parts of the memory manager.
 #