arm: dts: socfpga*.dts*: use SPDX-License-Identifier

Follow the recent trend for the license description.

This is also in an effort to fully sync the devicetrees with U-Boot.

Signed-off-by: Simon Goldschmidt <simon.k.r.goldschmidt@gmail.com>
Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>

arch/arm/boot/dts/socfpga_vt.dts

@@ -1,18 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0+
 /*
- *  Copyright (C) 2013 Altera Corporation <www.altera.com>
- *
- * 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.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ * Copyright (C) 2013 Altera Corporation <www.altera.com>
  */
 
 /dts-v1/;