Mesa 21.2 Lands NVIDIA's Code For Handling Alternate GBM Backends

Earlier this year was the proposed NVIDIA code from NVIDIA for allowing Mesa's GBM to support alternative back-ends. This support is notable given that most Wayland compositors are catering to using Mesa's Generic Buffer Manager (GBM) rather than EGLStreams or other options for buffer management. That support code has now been merged into Mesa 21.2...