sunxi: Normalise FEL support

Make sunxi's FEL code fit with the normal U-Boot boot sequence instead of
creating its own. There are some #ifdefs required in start.S. Future work
will hopefully remove these.

This series is available at u-boot-dm, branch sunxi-working.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>