Should be:
dtc -O dtb -o /tmp/image/boot/dtb/allwinner/sun50i-a64-sopine-baseboard.dtb -b 0 sun50i-a64-sopine-baseboard.dts
Not that I'm critiquing or anything, I hope you got that new brain for your birthday
Anyway, I can also confirm that this is indeed working. My clusterboard thanks you!