cros_bundle_firmware: Provide a default textbase
cros_bundle_firmware: Provide a default textbase

When the fdt does not specify the textbase, we can read it from the
U-Boot image anyway. So use a default of zero.

BUG=chromium-os:32468
TEST=manual
run cros_bundle_firmware using a device tree file without a textbase
property in chromeos-config. See that it no longer fails.

Change-Id: Ic20f0284226ad8b473e3e5a33c53ed16381262eb
Reviewed-on: https://gerrit.chromium.org/gerrit/27158
Reviewed-by: Rhyland Klein <9c6f026f68ffecc44f215af186ef513cd72b6ce4@nvidia.com>
Reviewed-by: Che-Liang Chiou <57969107b634cf11cb64e9d768fd46929066adab@chromium.org>
Commit-Ready: Simon Glass <c00b0378376498bd9cd974c388df8854c0131d27@chromium.org>
Tested-by: Simon Glass <c00b0378376498bd9cd974c388df8854c0131d27@chromium.org>

mgireesh05/dev-util,coreos/dev-util,mgireesh05/dev-util,marineam/coreos-dev-util,mgireesh05/dev-util,coreos/dev-util,coreos/dev-util,marineam/coreos-dev-util