wl1251 supports also that NVS is stored in a separate EEPROM, add support
for that.

kvalo: use platform data instead Kconfig and use kernel style
Signed-off-by: David-John Willis <John.Willis@Distant-earth.com>
Signed-off-by: Kalle Valo <kalle.valo@nokia.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>