Some i.MX boards which use device tree to describe the hardware
for U-Boot generate a u-boot-dtb.imx binary.
Introduce the BR2_TARGET_UBOOT_FORMAT_DTB_IMX option to
handle such case.
Signed-off-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>