iwlwifi: remove ucode virtual functions

AGN devices all use the same ucode operations,
except for 4965, because 4965 uses only v1 file
headers.

Therefore, we can remove all the indirection
we have here and just code the API distinction
in place, with a small special case for 4965.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>