IB/mlx5: Move hardware counters initialization to the corresponding stage

Now that we have a stage just for hardware counters, move all relevant
initialization logic into one place.

Signed-off-by: Mark Bloch <markb@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>