mb/google/rex: Add FW_CONFIG* to Kconfig

BUG=b:253199788
TEST=Build and boot to Google/Rex.

Change-Id: Ib729c98a4d67aa46992fdccf592010b0313605a6
Signed-off-by: Eran Mitrani <mitrani@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/66817
Reviewed-by: Tarun Tuli <taruntuli@google.com>
Reviewed-by: Subrata Banik <subratabanik@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/google/rex/Kconfig

@@ -11,6 +11,8 @@ config BOARD_GOOGLE_REX_COMMON
 	select EC_GOOGLE_CHROMEEC_BOARDID
 	select EC_GOOGLE_CHROMEEC_ESPI
 	select EC_GOOGLE_CHROMEEC_SKUID
+	select FW_CONFIG
+	select FW_CONFIG_SOURCE_CHROMEEC_CBI
 	select HAVE_ACPI_RESUME
 	select HAVE_ACPI_TABLES
 	select I2C_TPM