drm/virtio: implement blob resources: blob display integration

SCANOUT_BLOB forwards the DRM framebuffer metadata to the host. The
modifier is intentionally left out -- it may be possible to query
the host for that.

We also assume one blob resource per DRM framebuffer.  That too is
an intentional simplification.

Signed-off-by: Gurchetan Singh <gurchetansingh@chromium.org>
Acked-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20200924003214.662-14-gurchetansingh@chromium.org


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