spl: Plumb in the Universal Payload handoff

Specify the FIT and include information about each loaded image, as
required by the UPL handoff.

Write the UPL handoff into the bloblist before jumping to the next phase.

Control this using a runtime flag to avoid conflicting with other
handoff mechanisms.

Signed-off-by: Simon Glass <sjg@chromium.org>
4 files changed