iwlwifi: cleanup references to 8000 family in NVM code

NVM code is tightly coupled with 8000 family, while
it really refers to extended NVM format introduced
back then. Separate it to a configuration dependent
boolean, and rename defines accordingly.

Signed-off-by: Sara Sharon <sara.sharon@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>