mpc8323erdb: fix EEPROM page size and get MAC from EEPROM

This patch fixes eeprom page size so that you can now write more than
64 bytes at a time.

It also makes the board take MAC addresses, if found, from EEPROM.

User should place up to 4 addresses at offset 0x7f00, for
eth{,1,2,3}addr.  Any unused addresses should be zero.  This group of
four six-byte values should have it's CRC at the end.  crc32 and
eeprom commands can be used to accomplish this.

If CRC fails, MAC addresses come from the environment.  If CRC
succeeds, the environment is overwritten at startup.

Signed-off-by: Michael Barkowski <michael.barkowski@freescale.com>
Signed-off-by: Kim Phillips <kim.phillips@freescale.com>