mainboard/siemens: Use SPDX for GPL-2.0-only files

Done with sed and God Lines. Only done for C-like code for now.

Change-Id: I7b656f0244774cb174a90d97c5ae1c725802b636
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/40099
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: HAOUAS Elyes <ehaouas@noos.fr>
diff --git a/src/mainboard/siemens/mc_apl1/variants/mc_apl2/mainboard.c b/src/mainboard/siemens/mc_apl1/variants/mc_apl2/mainboard.c
index e6aff80..1aa5fb2 100644
--- a/src/mainboard/siemens/mc_apl1/variants/mc_apl2/mainboard.c
+++ b/src/mainboard/siemens/mc_apl1/variants/mc_apl2/mainboard.c
@@ -1,16 +1,5 @@
-/*
- * This file is part of the coreboot project.
- *
- *
- * 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. */
 
 #include <bootstate.h>
 #include <console/console.h>