mailbox/omap: switch to SPDX license identifier

Use the appropriate SPDX license identifier in the OMAP Mailbox
driver source files and drop the previous boilerplate license text.

Signed-off-by: Suman Anna <[e-mail]>
Signed-off-by: Jassi Brar <[e-mail]>

drivers/mailbox/omap-mailbox.c

···
+// SPDX-License-Identifier: GPL-2.0
 /*
  * OMAP mailbox driver
  *
···
  *
  * Contact: Hiroshi DOYU <[e-mail]>
  *          Suman Anna <[e-mail]>
- *
- * 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.
- *
- * 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>

include/linux/omap-mailbox.h

···
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * omap-mailbox: interprocessor communication module for OMAP
- *
- * 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.
  */
 
 #ifndef OMAP_MAILBOX_H