https://github.com/u-boot/u-boot <= mainline u-boot source. The current 2020.01 release supports VIM1/2/3 and commits to support VIM3L are in the master branch ready for 2020.04 release.
https://github.com/LibreELEC/amlogic-boot-fip <= all the fip sources for easy distro packaging if you want to build u-boot like LE does. You’ll find the fip recipe(s) in my branch of the LE repo too.
mainline u-boot is not as fully featured as the BSP one (as usual) but there’s not a lot missing and it’s more than enough support for Manjaro and other distros to use things. Neil generally syncs the device trees and adds larger features once they’ve been through a couple of kernel cycles and are considered stable. He’s also one of the designated maintainers for Amlogic now, so getting things merged is fairly simple compared to a year or so ago. Contributions are encouraged!