board: am57xx: fit: add support for selecting dtb dynamically

FIT allows for a multiple dtb in a single image. SPL needs away to
detect the right dtb to be used. Adding support for the same for am57xx
platforms.

Reviewed-by: Tom Rini <trini@konsulko.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
1 file changed