iwlwifi: port to cfg80211 rfkill

This ports the iwlwifi rfkill code to the new API offered by
cfg80211 and thus removes a lot of useless stuff. The soft-
rfkill is completely removed since that is now handled by
setting the interfaces down.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Tested-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>