drm/virtio: implement context init: probe for feature

Let's probe for VIRTIO_GPU_F_CONTEXT_INIT.

Create a new DRM_INFO(..) line since the current one is getting
too long.

Signed-off-by: Anthoine Bourgeois <anthoine.bourgeois@gmail.com>
Acked-by: Lingfeng Yang <lfy@google.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20210921232024.817-5-gurchetansingh@chromium.org


Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>