Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/arch/sparc/kernel/nmi.c b/arch/sparc/kernel/nmi.c
index 8babbeb..060fff9 100644
--- a/arch/sparc/kernel/nmi.c
+++ b/arch/sparc/kernel/nmi.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 /* Pseudo NMI support on sparc64 systems.
  *
  * Copyright (C) 2009 David S. Miller <davem@davemloft.net>