uboot-imx

cmd: Add dtimg command

dtimg command allows user to work with Android DTB/DTBO image format.
Such as, getting the address of desired DTB/DTBO file, printing the dump
of the image in U-Boot shell, etc.

This command is needed to provide Android boot with new Android DT image
format further.

Signed-off-by: Sam Protsenko <semen.protsenko@linaro.org>
Reviewed-by: Tom Rini <trini@konsulko.com>