make_dev_ssd: support new %U parameter
make_dev_ssd: support new %U parameter

The %U is better since arm and x86 both supports it now.

BUG=chromium-os:15683
TEST=./make_dev_ssd.sh # need latest kernel patch

Change-Id: I94a6471788d3496cfa7ef263493e89877bb2b593
Reviewed-on: http://gerrit.chromium.org/gerrit/3551
Reviewed-by: Che-Liang Chiou <57969107b634cf11cb64e9d768fd46929066adab@chromium.org>
Tested-by: Hung-Te Lin <8a7fce4940baad93a69f5073b383c85deed9d9c4@chromium.org>

acorn-marvell/vboot_reference,geekboxzone/mmallow_external_vboot_reference,ccaapton/vboot_reference,coreboot/vboot,geekboxzone/mmallow_external_vboot_reference,marineam/seismograph,coreboot/vboot,acorn-marvell/vboot_reference,marineam/seismograph,acorn-marvell/vboot_reference,ionave/seismograph,marineam/seismograph,coreboot/vboot,coreboot/vboot,ionave/seismograph,coreboot/vboot,geekboxzone/mmallow_external_vboot_reference,ccaapton/vboot_reference,geekboxzone/mmallow_external_vboot_reference,geekboxzone/mmallow_external_vboot_reference,ionave/seismograph,acorn-marvell/vboot_reference,marineam/seismograph,ccaapton/vboot_reference,ccaapton/vboot_reference