ec, lib, security, sb: Add SPDX license headers to Kconfig files

Change-Id: Ie63499a4b432803a78af1c52d49e34cf1653ba17
Signed-off-by: Martin Roth <gaumless@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/80589
Reviewed-by: Felix Singer <service+coreboot-gerrit@felixsinger.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/lib/Kconfig

@@ -1,3 +1,5 @@
+## SPDX-License-Identifier: GPL-2.0-only
+
 config MISSING_BOARD_RESET
 	bool
 	help