gpio: lpc18xx: use SPDX license identifier

Replace GPLv2 header with the SPDX identifier.
Signed-off-by: Vladimir Zapolskiy <vz@mleia.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpio-lpc18xx.c

+// SPDX-License-Identifier: GPL-2.0
 /*
  * GPIO driver for NXP LPC18xx/43xx.
  *
  * Copyright (C) 2015 Joachim Eastwood <manabian@gmail.com>
  *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License version 2 as
- * published by the Free Software Foundation.
- *
  */
 
 #include <linux/clk.h>