Three-chain devices are using a different
EEPROM layout than the rest of the chipsets.
Add a new map which describes the new layout
and use that for the RT3593 chipset.

The index values has been computed from the
EEPROM_EXT_* defines, which can be found in
the 'include/chip/rt3593.h' file in the
Ralink DPO_RT5572_LinuxSTA_2.6.0.1_20120629
driver.
Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Acked-by: Stanislaw Gruszka <stf_xl@wp.pl>
Acked-by: Gertjan van Wingerde <gwingerde@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>