mach-sunxi: Enable SPI boot for SUNIV and licheepi nano

Enable SPI boot in SPL on SUNIV architecture and use
it in the licheepi nano that uses the F1C100s.

Signed-off-by: Jesse Taube <Mr.Bossman075@gmail.com>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>