net: dsa: mv88e6171: Add other members of the family

The 6171 is one member of the family 6171/6175/6350/6351. Add the
other family members to the driver.

Not tested on these new devices.

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