net/mlx4: Use devl_ API for devlink port register / unregister

Use devl_ API to call devl_port_register() and devl_port_unregister()
instead of devlink_port_register() and devlink_port_unregister(). Add
devlink instance lock in mlx4 driver paths to these functions.

This will be used by the downstream patch to invoke mlx4 devlink reload
callbacks with devlink lock held.

Signed-off-by: Moshe Shemesh <moshe@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>