Hmm I always assumed that there were missing/unsolved pieces of the driver that would need to be fixed first, based on the way that support for these devices seems to need to be solved one by one [0] but it looks like at least someone has made progress on a different board [1]

[0] ayufan https://docs.google.com/spreadsheets/d/1pCqJg0VSzvihUOoxCOq3...

[1] https://www.reddit.com/r/arm/comments/9v8qpm/do_amd_or_nvidi...

Last I saw the chipset can't map enough memory space to PCIe for GPUs to work, but this might be possible to change with a firmware update.