util: Add SPDX header, replacing boiler plate where applicable

In a few cases a license was added: Stuff coming from Linux is
"GPL-2.0" (not GPL-2.0-only!), build-release is by me and got the
usual GPL-2.0-only treatment. uio_usbdebug and spkmodem had their
licenses propagate to all their files.

Change-Id: Ia5712bbaa417cb9e937834512351fcc0acfa16be
Signed-off-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/41202
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: HAOUAS Elyes <ehaouas@noos.fr>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

util/superiotool/Makefile

@@ -1,14 +1,4 @@
-##
-## 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
 
 PROGRAM = superiotool