drm/virtio: implement blob resources: fix stride discrepancy

The old transfer ioctls may work on blob resources, and there is no
TRANSFER_BLOB hypercall now for simplicity.

The guest may have a image view on the blob resources such that the
stride is not equal to width * bytes_per_pixel.

For host-only blobs, we can repurpose the transfer ioctls to synchronize
caches as well.  For guest-only blobs, these operations are undefined
for now so leave them out.

Also, with seamless Wayland integration between guest/host looking
increasingly attractive, it also makes sense to keep track of
one value for stride.

Signed-off-by: Gurchetan Singh <gurchetansingh@chromium.org>
Acked-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20200924003214.662-16-gurchetansingh@chromium.org


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