platforms/drm: support NVidia as secondary GPU with CPU copy
If the proprietary NVidia driver allows presentation with dumb buffers (I assume it does) this should allow for multi-GPU operation with Intel or AMD as primary GPU. This is especially important for a lot of laptops where the ports for external displays are wired to the dedicated NVidia GPU and not to the integrated one.
Would be nice if someone could test this, I don't have the hardware to do that.