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/gpu/drm/cirrus/Kconfig

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: GPL-2.0-only
 config DRM_CIRRUS_QEMU
 	tristate "Cirrus driver for QEMU emulated device"
 	depends on DRM && PCI && MMU

drivers/gpu/drm/cirrus/Makefile

@@ -1 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-only
 obj-$(CONFIG_DRM_CIRRUS_QEMU) += cirrus.o