Uncommented VIRTIO_GPU_F_VIRGL (bit 0) and added feature
negotiation in probe_device(). When the host supports VirGL 3D,
the driver now acknowledges the feature, enabling Mesa's virgl
driver to use the 3D command path (CTX_CREATE, SUBMIT_3D,
RESOURCE_CREATE_3D, etc. already defined in CommandTy enum).
Cross-referenced with Linux 7.1 drivers/gpu/drm/virtio/virtgpu_drv.c
virtio_gpu_driver_open() and virtio spec v1.2 §5.7.6.
This is the enabling step for hardware-accelerated 3D rendering
in QEMU via virglrenderer.
Red Bear OS