vdpa/mlx5: add VM memory registration task

vdpa/mlx5: add VM memory registration task

The driver creates a direct MR object of
the HW for each VM memory region,
which maps the VM physical address to
the actual physical address.

Later, after all the MRs are ready,
the driver creates an indirect MR to group all the direct MRs
into one virtual space from the HW perspective.

Create direct MRs in parallel using the MT mechanism.
After completion, the primary thread creates the indirect MR
needed for the following virtqs configurations.

This optimization accelerrate the LM process and
reduce its time by 5%.

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