net: dsa: qca8k: add ethernet-ports fallback to setup_mdio_bus

Dsa now also supports ethernet-ports. Add this new binding as a fallback
if the ports node can't be found.

Signed-off-by: Ansuel Smith <ansuelsmth@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>