rt2x00: rt2800lib: introduce local EEPROM access functions

The patch adds rt2800 specific functions for
EEPROM data access and changes the code to use
these instead of the generic rt2x00_eeprom_*
variants.

To avoid functional changes, the new functions
are wrappers around the corresponding generic
rt2x00_eeprom_* routines for now. Functional
changes will be implemented in additional patches.

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>