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/soc/bcm/brcmstb/Kconfig

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: GPL-2.0-only
 if SOC_BRCMSTB
 
 config BRCMSTB_PM

drivers/soc/bcm/brcmstb/Makefile

@@ -1,2 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0-only
 obj-y				+= common.o biuctrl.o
 obj-$(CONFIG_BRCMSTB_PM)	+= pm/

drivers/soc/bcm/brcmstb/pm/Makefile

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: GPL-2.0-only
 obj-$(CONFIG_ARM)		+= s2-arm.o pm-arm.o
 AFLAGS_s2-arm.o			:= -march=armv7-a
 obj-$(CONFIG_BMIPS_GENERIC)	+= s2-mips.o s3-mips.o pm-mips.o