watchdog: imx2_wdt: Switch to SPDX identifier

Adopt the SPDX license identifier headers to ease license compliance
management.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>

drivers/watchdog/imx2_wdt.c

@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Watchdog driver for IMX2 and later processors
  *
@@ -7,10 +8,6 @@
  * some parts adapted by similar drivers from Darius Augulis and Vladimir
  * Zapolskiy, additional improvements by Wim Van Sebroeck.
  *
- * 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.
- *
  * NOTE: MX1 has a slightly different Watchdog than MX2 and later:
  *
  *			MX1:		MX2+: