v3d, vc4: Fix dmabuf import for non-scanout buffers

v3d, vc4: Fix dmabuf import for non-scanout buffers

Failure to create a buffer for scanout should not be fatal when
importing a buffer. Buffers allocated from a render-only device may not
be able to scanned out directly but can still be used for other
rendering purposes (e.g. as a texture).

Signed-off-by: Joshua Watt <JPEWhacker@gmail.com>
Reviewed-by: Simon Ser <contact@emersion.fr>
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Cc: mesa-stable
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12081>