lantiq: Fixes to athxk EEPROM loading

Use platform data array for storing ath5k EEPROM instead of creating another one.
EEPROM size is 2048 words (2 bytes), so we must read 4096 bytes from flash.
No need to keep the checksum fix now that the EEPROM is loaded completely.
Add a manual eeprom swap for ath9k and keep the endian way.
Use mac-offset property retrieved from the DTS.

Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>

SVN-Revision: 36901