src/superio: replace license boilerplate with SPDX

The authors from the header of the files are added in a previous commit.

Change-Id: Iafeaafb9689c65bd2f5de3960097ec0d4c1009e7
Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/38544
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/src/superio/smsc/lpc47n227/superio.c b/src/superio/smsc/lpc47n227/superio.c
index 911343d..923a766 100644
--- a/src/superio/smsc/lpc47n227/superio.c
+++ b/src/superio/smsc/lpc47n227/superio.c
@@ -1,18 +1,5 @@
-/*
- * This file is part of the coreboot project.
- *
- * Copyright (C) 2005 Digital Design Corporation
- * Copyright (C) 2008-2009 coresystems GmbH
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation; version 2 of the License.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- */
+/* SPDX-License-Identifier: GPL-2.0-only */
+/* This file is part of the coreboot project. */
 
 /* RAM-based driver for SMSC LPC47N227 Super I/O chip. */