dtb/allwinner: Add sun7i-a20-lamobo-r1.dts (Banana Pi R1)

FreeBSD boots on this board, but the ethernet switch is not currently
supported, resulting in no ethernet.

A U-Boot port will be added once the ethernet switch is at least basically
supported, but we add its DTS to the build here to lower the barrier-to-boot
while work is underway.