U-Boot does not yet have SPL code to initialize the DDR controller on the
Allwinner D1 - So instead package the sun20i-d1-spl bootloader, which is
based on boot0 from the Allwinner BSP with some modifications to build it
separately from the BSP and boot mainline U-Boot as explained on the
linux-sunxi wiki:
https://linux-sunxi.org/Allwinner_Nezha
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
