vdpa/mlx5: support pre-creation of virtq resource

vdpa/mlx5: support pre-creation of virtq resource

The motivation of this change is to reduce vDPA device queue creation
time by creating some queue resource in vDPA device probe stage.

In VM live migration scenario, this can reduce 0.8ms for each queue
creation, thus reduce LM network downtime.

To create queue resource(umem/counter) in advance, we need to know
virtio queue depth and max number of queue VM will use.

Introduce two new devargs: queues(max queue pair number) and queue_size
(queue depth). Two args must be both provided, if only one argument
provided, the argument will be ignored and no pre-creation.

The queues and queue_size must also be identical to vhost configuration
driver later receive. Otherwise either the pre-create resource is wasted
or missing or the resource need destroy and recreate(in case queue_size
mismatch).

Pre-create umem/counter will keep alive until vDPA device removal.

Signed-off-by: Yajun Wu <yajunw@nvidia.com>
Acked-by: Matan Azrad <matan@nvidia.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>