dt-bindings: pinctrl: samsung: Add SPDX license identifier

Replace GPL license statement with SPDX license identifier (GPL-2.0).
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>

include/dt-bindings/pinctrl/samsung.h

+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Samsung's Exynos pinctrl bindings
  *
  * Copyright (c) 2016 Samsung Electronics Co., Ltd.
  *		http://www.samsung.com
  * Author: Krzysztof Kozlowski <krzk@kernel.org>
- *
- * 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.
-*/
+ */
 
 #ifndef __DT_BINDINGS_PINCTRL_SAMSUNG_H__
 #define __DT_BINDINGS_PINCTRL_SAMSUNG_H__