mb/google/brya/var/yaviks: select USE_MTCL only if CHROMEOS

There is no wifi_mtcl.bin file publicly available, nor can it be
extracted from the stock Google firmware for YAVIKS, so restrict
USE_MTCL to downstream ChromeOS builds since validate_mtcl() fails
when no file is present in CBFS.

TEST=build/boot yaviks, verify no MTCL error in cbmem

Change-Id: I450db6fd8c460109aa4e491d88ec874c5f6429d0
Signed-off-by: Matt DeVillier <matt.devillier@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/90734
Reviewed-by: Eric Lai <ericllai@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Alicja Michalska <ahplka19@gmail.com>
Reviewed-by: Paul Menzel <paulepanter@mailbox.org>

src/mainboard/google/brya/Kconfig

@@ -771,7 +771,7 @@ config BOARD_GOOGLE_YAVIKS
 	select EC_GOOGLE_CHROMEEC_INCLUDE_SSFC_IN_FW_CONFIG
 	select HAVE_WWAN_POWER_SEQUENCE
 	select INTEL_GMA_HAVE_VBT
-	select USE_MTCL
+	select USE_MTCL if CHROMEOS
 
 config BOARD_GOOGLE_YAVILLA
 	select BOARD_GOOGLE_BASEBOARD_NISSA