media: rc keymaps: add SPDX identifiers to the code I wrote

As we're now using SPDX identifiers, on the several
RC keymap files I wrote, add the proper SPDX, identifying
the license I meant.

As we're now using the short license, it doesn't make sense to
keep the original license text.

Also, fix MODULE_LICENSE to identify GPL v2, as this is the
minimal license requirement for those modles.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

drivers/media/rc/keymaps/rc-adstech-dvb-t-pci.c

@@ -1,14 +1,9 @@
-/* adstech-dvb-t-pci.h - Keytable for adstech_dvb_t_pci Remote Controller
- *
- * keymap imported from ir-keymaps.c
- *
- * Copyright (c) 2010 by Mauro Carvalho Chehab
- *
- * 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.
- */
+// SPDX-License-Identifier: GPL-2.0+
+// adstech-dvb-t-pci.h - Keytable for adstech_dvb_t_pci Remote Controller
+//
+// keymap imported from ir-keymaps.c
+//
+// Copyright (c) 2010 by Mauro Carvalho Chehab
 
 #include <media/rc-map.h>
 #include <linux/module.h>