This guide is based on multiple guides as well as official instructions for the other boards found on the Internet:
- https://github.com/RoEdAl/alarm-uboot-sunxi-armv7
- https://uthings.uniud.it/building-mainline-u-boot-and-linux-kernel-for-orange-pi-boards
- https://archlinuxarm.org/platforms/armv7/allwinner/pcduino3
I have gone through all these steps recently and got a working board with my favorite Arch Linux ARM. I hope it will be helpful for someone else.