vdpa/mlx5: Allow creation of blank VQs

Based on the filled flag, create VQs that are filled or blank.
Blank VQs will be filled in later through VQ modify.

Downstream patches will make use of this to pre-create blank VQs at
vdpa device creation.

Signed-off-by: Dragos Tatulea <dtatulea@nvidia.com>
Reviewed-by: Cosmin Ratiu <cratiu@nvidia.com>
Message-Id: <20240626-stage-vdpa-vq-precreate-v2-15-560c491078df@nvidia.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Eugenio Pérez <eperezma@redhat.com>
Acked-by: Eugenio Pérez <eperezma@redhat.com>