So far msdk produced dmabuf fds are non-mappable.
If user wants to download the content of underlined surfaces,
dmabufcapsfeature negotiated pipeline will fail. So if the input surface
is dmabuf and downstream doesn't have support for dmabuf capsfeatures,
we do the vpp (no passthrough) and produce the mappable videomemory
buffers.
https://bugzilla.gnome.org/show_bug.cgi?id=794946
e1a90f1ec9