iwlwifi: validate the signature for EEPROM and OTP

Both 1000 & 6000 series NICs contain on-chip OTP memory that
replaces the off-chip EEPROM memory. The nature of OTP means
there is a limited number of times a particular board can go through the
factory flow and be (re)calibrated. As a consequence there will be some boards
that contain EEPROM memory because OTP blocks were full.

In the signature validation routine, iwlwifi needs to make sure
"select bit" and "EEPROM/OTP signature" agree on the type of
NVM to be used to configure the system.

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>