iwlwifi: mvm: Prioritize external nvm values on top of the OTP values

Read first the nvm sections from the OTP, then read the nvm
sections from the external file and override the OTP values
(if there were any values in the OTP).

Signed-off-by: Eran Harary <eran.harary@intel.com>
Reviewed-by: Dor Shaish <dor.shaish@intel.com>
Reviewed-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>