uboot-imx

MLK-19123-4 fastboot: Enable uuu for i.MX6DL sabre

i.MX6DL boards enable fastboot as default, support both sabresd and
sabreauto.
uuu will use fastboot command to write emmc.

Signed-off-by: Xiaoning Wang <xiaoning.wang@nxp.com>
Signed-off-by: Ye Li <ye.li@nxp.com>