Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/arch/nios2/platform/Makefile b/arch/nios2/platform/Makefile
index 46364f1..fb5bdb4 100644
--- a/arch/nios2/platform/Makefile
+++ b/arch/nios2/platform/Makefile
@@ -1 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-only
 obj-y += platform.o