I returned to this project after some time. If there are people still interested in this small POE capable board, I have created a repository with armbian userpatches and build instructions. There is also binary firmware (built from current main - 23.11) available for download on the release page.
https://github.com/loblik/bananapi-p2-zero-dts
If you find some bugs, you can file an issue on github.
I've also sent device tree patches upstream again.