lantiq: do an endianness swap to the RT2860 eeprom for ARV752DPW(22)

lantiq: do an endianness swap to the RT2860 eeprom for ARV752DPW(22)

ARV7510PW22, ARV752DPW and ARV752DPW22 have the RT2860 eeprom stored in
flash as big-endian, but the driver needs it in little-endian format. We
have to swab it before handing it over. This requires my earlier patch
for busybox.

Funnily enough, ARV752DPW works also with the incorrect eeprom, but
undoubtedly unoptimally. I have a hunch that also the final remaining
Lantiq board would require this swabbing, but I'm not sure, so I just
swab it in the three boards that I know about.

v2:
* Swab also on ARV7510PW22 based on feedback from Alvaro Rojas
* Fix the offset with bs=2

Signed-off-by: Matti Laakso <malaakso at elisanet.fi>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@40328 3c298f89-4303-0410-b956-a3cf2f4a3e73