treewide: more SPDX header work

Change-Id: Ib78c322730ec6dfa9dcaafa16e5741cd3d351b8d
Signed-off-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/41174
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Martin Roth <martinroth@google.com>
Reviewed-by: HAOUAS Elyes <ehaouas@noos.fr>

Makefile.inc

@@ -1,17 +1,5 @@
-##
-## This file is part of the coreboot project.
-##
-## Copyright (C) 2011 secunet Security Networks AG
-##
-## 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.
-##
+# This file is part of the coreboot project.
+# SPDX-License-Identifier: GPL-2.0-only
 
 ifneq ($(NOCOMPILE),1)
 GIT:=$(shell git -C "$(top)" rev-parse --git-dir 1>/dev/null 2>&1 \