Your kernel stack trace looks similar to mine with an RX480 under a recent 5.8.x kernel. I solved that oops in the power management routines by turning power management off. Append "amdgpu.runpm=0 amdgpu.bapm=0 amdgpu.dpm=0 amdgpu.aspm=0" to your kernel boot parameters. In addition, you might also try to add "amdgpu.dc=0" which disables some new DisplayCore code for AMD GPU.