backends/drm: don't attempt multi GPU copies with unsupported formats
Specifically with the proprietary Nvidia driver, the plane requires a linear modifier, which we can't render to with OpenGL. When attempting to render with that buffer, we end up logging errors at a really high rate, and falling back to a software cursor rather than another import mode.
This only targets 6.6 because the MultiGpuSwapchain in master already takes care of this. Note that !9158 (merged) is required for the hardware cursor to work again with Nvidia as the secondary GPU, since the dmabuf mode also fails too late for the fallback to work.