vdpa/mlx5: cache and reuse hardware resources

vdpa/mlx5: cache and reuse hardware resources

During device suspend and resume, resources are not changed normally.
When huge resources were allocated to VM, like huge memory size or lots
of queues, time spent on release and recreate became significant.

To speed up, this patch reuses resources like VM MR and VirtQ memory if
not changed.

Signed-off-by: Xueming Li <xuemingl@nvidia.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>