octeontx2: Move devlink registration to be last devlink command

This change prevents from users to access device before devlink is fully
configured. This change allows us to delete call to devlink_params_publish()
and impossible check during unregister flow.

Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>