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>

src/superio/ite/common/early_serial.c

@@ -1,19 +1,5 @@
-/*
- * This file is part of the coreboot project.
- *
- * Copyright (C) 2013 Damien Zammit <damien@zamaudio.com>
- * Copyright (C) 2014 Edward O'Callaghan <eocallaghan@alterapraxis.com>
- *
- * 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; either version 2 of the License, or
- * (at your option) any later version.
- *
- * 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-or-later */
+/* This file is part of the coreboot project. */
 
 #include <arch/io.h>
 #include <device/pnp_ops.h>