tools: sunxi: Add spl image builder

tools: sunxi: Add spl image builder

This program generates raw SPL images that can be flashed on the NAND with
the ECC and randomizer properly set up.

This has been copied (and tweaked to find the right headers) from the
sunxi-tools (https://github.com/linux-sunxi/sunxi-tools) upstream
repository, commit 1c3a6ca5.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Acked-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Jagan Teki <jagan@openedev.com>