Fix ugly hack to disable 'AMD SUMO' GPU.

[coryan]

On coryan@'s workstation the default GPU device is 'AMD SUMO', unfortunately this is a very underpowered GPU, it cannot handle any of the interesting tests, at least not with the amdgpu open source driver.

I put a hack in place to fallback to the best available GPU if AMD SUMO is returned. That should work as long as the workstation has a discrete GPU better than AMD SUMO. It should also work on workstations that do not have a AMD SUMO device, and should work on VMs or containers where the only device is a pocl-based CPU.

However, the hack is still pretty ugly and I would like to fix it in a better way, I just do not know of any.