rtc: xgene: convert to SPDX identifier

Use SPDX-License-Identifier instead of a verbose license text.
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

drivers/rtc/rtc-xgene.c

+// SPDX-License-Identifier: GPL-2.0+
 /*
  * APM X-Gene SoC Real Time Clock Driver
  *
  * Copyright (c) 2014, Applied Micro Circuits Corporation
  * Author: Rameshwar Prasad Sahu <rsahu@apm.com>
  *         Loc Ho <lho@apm.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/>.
- *
  */
 
 #include <linux/init.h>