arm: dts: zynq: Use SPDX-License-Identifier

Follow trend and use the SPDX License description.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>

arch/arm/boot/dts/zynq-zc702.dts

@@ -1,15 +1,7 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  *  Copyright (C) 2011 - 2014 Xilinx
  *  Copyright (C) 2012 National Instruments Corp.
- *
- * This software is licensed under the terms of the GNU General Public
- * License version 2, as published by the Free Software Foundation, and
- * may be copied, distributed, and modified under those terms.
- *
- * 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.
  */
 /dts-v1/;
 #include "zynq-7000.dtsi"