cros_bundle_firmware: Add missing GBB flags

These can be set in the dts to change the image behavior.
It's particularly useful for testing.

BUG=none
TEST=Add gbb-flag-force-dev-boot-legacy to cros/dts/factory-friendly.dtsi
     and see that the default GBB flags are 0xb9 instead of 0x39
BRANCH=link

Change-Id: I504bd1f3b27a864798278a724c4ad467189ab81d
Reviewed-on: https://gerrit.chromium.org/gerrit/34791
Commit-Ready: Stefan Reinauer <reinauer@chromium.org>
Reviewed-by: Stefan Reinauer <reinauer@chromium.org>
Tested-by: Stefan Reinauer <reinauer@chromium.org>
1 file changed