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/Makefile.inc b/src/superio/smsc/Makefile.inc
index 9b86745..af43fef 100644
--- a/src/superio/smsc/Makefile.inc
+++ b/src/superio/smsc/Makefile.inc
@@ -1,18 +1,5 @@
-##
-## This file is part of the coreboot project.
-##
-## Copyright (C) 2009 Ronald G. Minnich
-## Copyright (C) 2012 Advanced Micro Devices, Inc.
-##
-## 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.
 
 subdirs-y += dme1737
 subdirs-y += fdc37n972