net: dsa: mv88e6xxx: Add the mv88e6390 family

With the devices added to the tables, the probe will recognize the
switch. This however is not sufficient to make it work properly, other
changes are needed because of incompatibilities.

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