ARM: at91/dt: add ethernet phy to at91rm9200ek board

Add ethernet phy node in at91rm9200ek.dts.
The reg register is not specified, as it may differ depending on the init
process of the board:
ADDR0/1 phy pins are connected to PA13/14 rm9200 pins. Which means the phy
will take its address from these pins during the reset process.

The macb driver will launch a full scan on the mdio bus to discover the phy
address.

Signed-off-by: Boris BREZILLON <b.brezillon@overkiz.com>
[nicolas.ferre@atmel.com: changed to IRQ_TYPE_EDGE_BOTH as asked by Boris]
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>