iwlwifi: support NVM access (EEPROM/OTP)

Two type of NVM available for devices 1000, 6000 and after, adding
support to read OTP lower blocks if OTP is used instead of EEPROM.

Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>