powerpc/dts/virtex440: Add ethernet phy to virtex440-ml507 board

This adds the marvel phy which is present on the ml507 board.
Without this ethtool causes kernel-oopses.

Tested on ml507 board.

Signed-off-by: Gernot Vormayr <gvormayr@gmail.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>