net/mlx5: Use xarray to store and manage completion EQs

Use xarray to store the completion EQs instead of a linked list.
The xarray offers more scalability, reduced memory overhead, and
facilitates the lookup of a certain EQ given a vector index.

Signed-off-by: Maher Sanalla <msanalla@nvidia.com>
Reviewed-by: Shay Drory <shayd@nvidia.com>
Reviewed-by: Moshe Shemesh <moshe@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>