Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/arch/x86/purgatory/stack.S b/arch/x86/purgatory/stack.S
index 50a4147..8b14274 100644
--- a/arch/x86/purgatory/stack.S
+++ b/arch/x86/purgatory/stack.S
@@ -1,10 +1,8 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
 /*
  * purgatory:  stack
  *
  * Copyright (C) 2014 Red Hat Inc.
- *
- * This source code is licensed under the GNU General Public License,
- * Version 2.  See the file COPYING for more details.
  */
 
 	/* A stack for the loaded kernel.