rpmsg: smd: Switch to SPDX license identifier

Use the appropriate SPDX license identifier in the rpmsg SMD backend
driver source file and drop the previous boilerplate license text.
Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>

drivers/rpmsg/qcom_smd.c

+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (c) 2015, Sony Mobile Communications AB.
  * Copyright (c) 2012-2013, The Linux Foundation. All rights reserved.
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License version 2 and
- * only version 2 as published by the Free Software Foundation.
- *
- * 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/interrupt.h>