drm/virtio: enqueue virtio_gpu_create_context after the first 3D ioctl

drm/virtio: enqueue virtio_gpu_create_context after the first 3D ioctl

For old userspace, initialization will still be implicit.

For backwards compatibility, enqueue virtio_gpu_cmd_context_create after
the first 3D ioctl.

v3: staticify virtio_gpu_create_context
    remove notify to batch vm-exit
v6: Remove nested 3D checks (emil.velikov):
      - unify 3D check in resource create
v7: Remove check when getting capabilities

Reviewed-by: Chia-I Wu <olvaffe@gmail.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Signed-off-by: Gurchetan Singh <gurchetansingh@chromium.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20200225000800.2966-4-gurchetansingh@chromium.org
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>