net: lan743x: remove unwanted interface select settings

Remove the MII/RGMII Selection settings in driver as it is preset
by the EEPROM and has the required configurations before the driver
loads for LAN743x.

Signed-off-by: Pavithra Sathyanarayanan <Pavithra.Sathyanarayanan@microchip.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>