Documentation: Add FIT payload documentation

Describe the new uImage.FIT loader.

Change-Id: I8b2060f2a63406669196bcbc190cc1511ae9fe94
Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Reviewed-on: https://review.coreboot.org/27253
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Philipp Deppenwiese <zaolin.daisuki@gmail.com>
3 files changed