net: dsa: mv88e6171: Add EEE support to the mv88e6172

The mv88e6172 has support for EEE. Check for the product ID and call
the common code if applicable.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: David S. Miller <davem@davemloft.net>