sunxi: Support building a SPL as a TOC0 image

sunxi: Support building a SPL as a TOC0 image

Now that mkimage can generate TOC0 images, and the SPL can interpret
them, hook up the build infrastructure so the user can choose which
image type to build. Since the absolute load address is stored in the
TOC0 header, that information must be passed to mkimage.

Signed-off-by: Samuel Holland <samuel@sholland.org>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>