net/mlx5: Use devl_ API in mlx5_esw_offloads_devlink_port_register

The function mlx5_esw_offloads_devlink_port_register() calls
devlink_port_register() and devlink_rate_leaf_create(). Use devl_ API to
call devl_port_register() and devl_rate_leaf_create() accordingly and
add devlink instance lock in driver paths to this function.

Similarly, use devl_ API to call devl_port_unregister() and
devl_rate_leaf_destroy() in mlx5_esw_offloads_devlink_port_unregister()
and ensure locking devlink instance lock on the paths to this function
too.

This will be used by the downstream patch to invoke
mlx5_devlink_eswitch_mode_set() with devlink lock held.

Signed-off-by: Moshe Shemesh <moshe@nvidia.com>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>