drm/virtio: Add DRM capset definition

Define DRM native context capset in the VirtIO-GPU protocol header.
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Reviewed-by: Rob Clark <robdclark@gmail.com>
Reviewed-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240714205502.3409718-1-dmitry.osipenko@collabora.com

include/uapi/linux/virtio_gpu.h

@@ -311,6 +311,7 @@ struct virtio_gpu_cmd_submit {
 #define VIRTIO_GPU_CAPSET_VIRGL2 2
 /* 3 is reserved for gfxstream */
 #define VIRTIO_GPU_CAPSET_VENUS 4
+#define VIRTIO_GPU_CAPSET_DRM 6
 
 /* VIRTIO_GPU_CMD_GET_CAPSET_INFO */
 struct virtio_gpu_get_capset_info {