dsa/mv88e6131: add support for mv88e6085 switch

The mv88e6085 is identical to the mv88e6095, except that all ports are
10/100 Mb/s, so use the existing setup code except for the cpu/dsa speed
selection in _setup_port().

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>
Acked-by: Lennert Buytenhek <buytenh@wantstofly.org>
Signed-off-by: David S. Miller <davem@davemloft.net>