powerpc/dts/virtex440: Declare address/size-cells for phy device

This fixes a warning:

  DTC     arch/powerpc/boot/virtex440-ml507.dtb
Warning (reg_format): "reg" property in /plb@0/xps-ll-temac@81c00000/ethernet@81c00000/phy@7 has invalid length (4 bytes) (#address-cells == 2, #size-cells == 1)
Warning (avoid_default_addr_size): Relying on default #address-cells value for /plb@0/xps-ll-temac@81c00000/ethernet@81c00000/phy@7
Warning (avoid_default_addr_size): Relying on default #size-cells value for /plb@0/xps-ll-temac@81c00000/ethernet@81c00000/phy@7

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Gernot Vormayr <gvormayr@gmail.com>
Cc: devicetree@vger.kernel.org
Cc: linuxppc-dev@lists.ozlabs.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>