lan78xx: Add to handle mux control per chip id

Depends on chip, some EEPROM pins are muxed with LED function.
Disable & restore LED function to access EEPROM.

Signed-off-by: Woojung Huh <woojung.huh@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>