spl: Plumb in the relocating loader

spl: Plumb in the relocating loader

This is fairly easy to use. The SPL loader sets up some fields in the
spl_image_info struct and calls spl_reloc_prepare(). When SPL is ready
to do the jump it must call spl_reloc_jump() instead of jump_to_image().

Add this logic.

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