gpio: vf610: Cut down on boilerplate

Just use the SPDX identifier for the license.
Acked-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpio-vf610.c

+// SPDX-License-Identifier: GPL-2.0+
 /*
  * Freescale vf610 GPIO support through PORT and GPIO
  *
  * Copyright (c) 2014 Toradex AG.
  *
  * Author: Stefan Agner <stefan@agner.ch>.
- *
- * 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.
  */
-
 #include <linux/bitops.h>
 #include <linux/err.h>
 #include <linux/gpio/driver.h>