uboot-imx

tools: add i.MX8/8X image support

i.MX8/8X bootable image type is container type.
The bootable image, containers a container set which supports two
container. The 1st container is for SECO firmware, the 2nd container
needs to include scfw, m4_0/1 image, ACore images per your requirement.

Signed-off-by: Peng Fan <peng.fan@nxp.com>