Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/drivers/char/apm-emulation.c b/drivers/char/apm-emulation.c
index 53436c0..230cf85 100644
--- a/drivers/char/apm-emulation.c
+++ b/drivers/char/apm-emulation.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 /*
  * bios-less APM driver for ARM Linux
  *  Jamey Hicks <jamey@crl.dec.com>