AMD R9 390 finally usable on Linux!

Yep, they definitely broke something, at one point (pre kernel 4.18.x) I had to use amdgpu.dpm=1 or my GPU would hang as soon as it tried to change power states, now I have remove it completely or my PC doesn’t get past the mode switch during boot up, there’s no performance issues without the switch though, so I guess they only half broke it.