m68knommu: Fixed GPIO pin initialization for CONFIG_M5271 FEC.

This processor only have one FEC and its MDIO pins are
located at a different offset than the code used for
the current CONFIG_M527x.

Tesed on M5271EVB eval platform.
Without this patch the FEC driver will report no PHY attached
if the bootloader does not pre-initialize the PAR_FECI2C GPIO register.

Signed-off-by: Richard Retanubun <RichardRetanubun@RuggedCom.com>
Signed-off-by: Greg Ungerer <gerg@uclinux.org>