net: ocelot: add support to get port mac from device-tree

Add support to get mac from device-tree using of_get_ethdev_address.

Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Clément Léger <clement.leger@bootlin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>