uboot-imx

tools: add i.MX8M image support

i.MX8M bootable image type is like i.MX6/7, but there is signed HDMI
firmware image in front of A53 bootable image, which is also has an IVT
header.

Here we also include fit image to generate a bootable image.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Stefano Babic <sbabic@denx.de>