Multi-GPU render device setting.

[axeljerabek]

Feature is related toa problem. My Intel Vaapi device is /dev/dri/render129 and not 128, which is the Nvidia GPU. I cannot set memories to use /dev/dri/render129 which would be the correct GPU for hardware accellerated transcoding via vaapi.

Describe the solution you'd like
Read out the /dev/dri render devices and let the user chose which one to use for which card and accelleration type: vaapi or nvenc.

Describe alternatives you've considered
none

Additional context
Add any other context or screenshots about the feature request here.