mb/google/brox: Disable EC/PD SW Sync

For initial debugging, we want to disable SW syncing.  Will re-enable
in the future.

BUG=b:300690448
BRANCH=None
TEST=emerge-brox coreboot chromeos-bootimage
     run gbb_utility --get --flags <image>
     make sure that it returns 0xa39

Change-Id: I865e9585ab37d1328a0ff54c6343cdad2c02220c
Signed-off-by: Shelley Chen <shchen@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/79569
Reviewed-by: Karthik Ramasubramanian <kramasub@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Keith Short <keithshort@chromium.org>

src/mainboard/google/brox/Kconfig

@@ -62,6 +62,8 @@ config BASEBOARD_DIR
 
 config CHROMEOS
 	select EC_GOOGLE_CHROMEEC_SWITCHES
+	select GBB_FLAG_DISABLE_EC_SOFTWARE_SYNC
+	select GBB_FLAG_DISABLE_PD_SOFTWARE_SYNC
 	select HAS_RECOVERY_MRC_CACHE
 
 config CHROMEOS_WIFI_SAR