net: dsa: mv88e6xxx: Add SERDES phydev_link_change for 6352

The 6352 family has one SERDES interface, which can be used by either
port 4 or port 5. Add interrupt support for the SERDES interface, and
report when the link status changes.

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