FreeBSD drm caught up with Linux 4.11 some months ago, and as shep mentioned,
it does include amdgpu, but obviously support goes as far as Polaris, no Vega unfortunately
. I think Linux' added Vega support in 4.15, which means the next major update has good chances of supporting it. However, the problem is that I don't see it happening any time soon,considering the frequency which the FreeBSD drm gets significant changes (once every 2 years or so)