Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/drivers/xen/manage.c b/drivers/xen/manage.c
index 5bb01a6..cd04668 100644
--- a/drivers/xen/manage.c
+++ b/drivers/xen/manage.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 /*
  * Handle extern requests for shutdown, reboot and sysrq
  */