Multi GPU support on Wayland
- refactor udev to list all available GPUs
- refactor DrmBackend to use the outputs of all GPUs
- create a new OpenGLBackend that contains multiple other backends
- enable EglGbmBackend to copy buffers from other GPUs
- make Atomic Mode Setting work properly on multiple GPUs (it doesn't on my secondary GPU)
- enable EglStreamBackend to copy buffers from other GPUs (!1031 (merged))
- enable EglStreamBackend to render outputs for other GPUs
To complete the support:
- enable automatic detection of the NVidia proprietary driver
- fix VSync on secondary GPUs
- enable hotplugging of GPUs
- add fallback mode with dumb buffers