iwlwifi: store cipher scheme independent of mac80211

In order to reduce reliance on mac80211 structs in the core
iwlwifi code, store the cipher schemes in the format given
by the firmware and convert it later, rather than storing it
in the mac80211 format.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>