omap: Devkit8000: Use DIE id to initialize dm9000 MAC address

The devkit8000 boards often come with empty EEPROM thus without
valid ethernet MAC address. The DIE id to MAC formula is copied from
u-boot.

Signed-off-by: Kan-Ru Chen <kanru@0xlab.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>