nfp: Implement ndo_get_port_parent_id()

NFP only supports SWITCHDEV_ATTR_ID_PORT_PARENT_ID, which makes it a
great candidate to be converted to use the ndo_get_port_parent_id() NDO
instead of implementing switchdev_port_attr_get().

Since NFP uses switchdev_port_same_parent_id() convert it to use
netdev_port_same_parent_id().

Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>