vdpa/mlx5: pre-create virtq at probing time

vdpa/mlx5: pre-create virtq at probing time

dev_config operation is called in LM progress.
LM time is very critical because all
the VM packets are dropped directly at that time.

Move the virtq creation to probe time and
only modify the configuration later in
the dev_config stage using the new ability
to modify virtq.

This optimization accelerates the LM process and
reduces its time by 70%.

Signed-off-by: Li Zhang <lizh@nvidia.com>
Acked-by: Matan Azrad <matan@nvidia.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>