xpedite1k: Remove support for reading MACs from EEPROM

By default, the XPedite1000 comes installed with xMon, a proprietary
bootloader.  xMon stores its MAC address in an onboard EEPROM.  Rather
than requiring a non-standard location in the EEPROM to be reserved for
MAC addresses, store the MAC addresses in U-Boot's standard environment.
A U-Boot application or OS application can be used to migrate xMon MAC
addresses to U-Boot's environment if necessary.

Signed-off-by: Peter Tyser <ptyser@xes-inc.com>
Signed-off-by: Stefan Roese <sr@denx.de>