google: veyron: CBFS_SIZE to match the available size for Coreboot in ChromeOS

When building for ChromeOS, it is expected that Coreboot will only occupy the
first MiB of the SPI flash, according to the veyron fmap description.
Otherwise, it makes sense to use the full ROM size.

Change-Id: I168386a5011222866654a496d8d054faff7a9406
Signed-off-by: Paul Kocialkowski <contact@paulk.fr>
Reviewed-on: http://review.coreboot.org/11117
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/mainboard/google/veyron/Kconfig

@@ -85,4 +85,9 @@ config PMIC_BUS
 	int
 	default 0
 
+config CBFS_SIZE
+	hex
+	default 0x100000 if CHROMEOS
+	default ROM_SIZE
+
 endif #  BOARD_GOOGLE_VEYRON