treewide: Add SPDX license identifier - Makefile/Kconfig

Add SPDX license identifiers to all Make/Kconfig files which:

 - Have no license information of any form

These files fall under the project license, GPL v2 only. The resulting SPDX
license identifier is:

  GPL-2.0-only

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/media/rc/Kconfig

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: GPL-2.0-only
 
 menuconfig RC_CORE
 	tristate "Remote Controller support"

drivers/media/rc/img-ir/Kconfig

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: GPL-2.0-only
 config IR_IMG
 	tristate "ImgTec IR Decoder"
 	depends on RC_CORE

drivers/media/rc/keymaps/Kconfig

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: GPL-2.0-only
 config RC_MAP
 	tristate "Compile Remote Controller keymap modules"
 	depends on RC_CORE