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/uio_usbdebug/linux/Makefile

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: GPL-2.0-only
 
 obj-m := uio_ehci_pci.o
 

util/uio_usbdebug/linux/uio_ehci_pci.c

@@ -1,16 +1,6 @@
 /* uio_ehci_pci - UIO driver for PCI EHCI devices */
-/*
- * This only implements MMIO access (no interrupts).
- *
- * 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 only implements MMIO access (no interrupts). */
+/* SPDX-License-Identifier: GPL-2.0-only */
 
 #include <linux/device.h>
 #include <linux/module.h>