iwlwifi: drop lib80211 dependency

Ever since Johannes' "iwlwifi: improve scan support" iwlwifi
no longer needs any of lib80211's functions or definitions.

This patch updates iwlwifi's Kconfig _selections_ and
removes all left lib80211.h inclusions from the source files.

Signed-off-by: Christian Lamparter <chunkeey@googlemail.com>
Acked-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>