net: bcmasp: Add support for PHY interrupts

Hook up the phy interrupts for internal phys to reduce mdio traffic
and improve responsiveness of link changes.

Signed-off-by: Justin Chen <justin.chen@broadcom.com>
Acked-by: Florian Fainelli <florian.fainelli@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>