I am excited to read about AllWinner support. How do I find out which devices are impacted? I have a Cubietruck (aka Cubieboard 3) and it would be great if I could run FreeBSD on it...
Look at ports/sysutils/u-boot-cubieboard2 for a template on how to build a suitable U-Boot, and sys/boot/fdt/dts/arm/cubieboard2.dts for a template for your dtb.
For a detailed list of supported hardware, have a look at the wiki: https://wiki.freebsd.org/FreeBSD/arm/Allwinner