mb/getac to mb/intel: Add SPDX license headers to Kconfig files

Change-Id: Id859c981d0bf5dcf90bf6858607a9fe726516309
Signed-off-by: Martin Roth <gaumless@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/80592
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Yidi Lin <yidilin@google.com>
Reviewed-by: Felix Singer <service+coreboot-gerrit@felixsinger.de>

src/mainboard/intel/mtlrvp/Kconfig

@@ -1,3 +1,5 @@
+## SPDX-License-Identifier: GPL-2.0-only
+
 config BOARD_INTEL_MTLRVP_COMMON
 	def_bool n
 	select BOARD_ROMSIZE_KB_32768