ocelot: Handle SWITCHDEV_PORT_OBJ_ADD/_DEL

Following patches will change the way of distributing port object
changes from a switchdev operation to a switchdev notifier. The
switchdev code currently recursively descends through layers of lower
devices, eventually calling the op on a front-panel port device. The
notifier will instead be sent referencing the bridge port device, which
may be a stacking device that's one of front-panel ports uppers, or a
completely unrelated device.

Dispatch the new events to ocelot_port_obj_add() resp. _del() to
maintain the same behavior that the switchdev operation based code
currently has. Pass through switchdev_handle_port_obj_add() / _del() to
handle the recursive descend, because Ocelot supports LAG uppers.

Register to the new switchdev blocking notifier chain to get the new
events when they start getting distributed.

Signed-off-by: Petr Machata <petrm@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>