arm: mvebu: 370-rd: Enable PHY interrupt handling

The Ethernet switch has an embedded interrupt controller. Interrupts
from the embedded PHYs are part of this interrupt controller.
Explicitly list the MDIO bus the embedded PHYs are on, and wire up the
interrupts.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>