drm/virtio: implement blob resources: report blob mem to userspace

The stride field has never been used, so repurpose it to be
"blob_mem". This way, userspace can know the memory properties
of the blob if it's passed between userspace processes and
no suitable userspace API exists to transmit that knowledge.

Signed-off-by: Gurchetan Singh <gurchetansingh@chromium.org>
Acked-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20200924003214.662-17-gurchetansingh@chromium.org


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