liquidio: Implement ndo_get_port_parent_id()

Liquidio 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().

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>