iwlwifi: unify iwlagn and 3945 power save management

This patch unifies 3945 and iwlagn power save management
This patch also better separates system state from user setting.
System state shall be removed later as this shall be shifted to user space

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Acked-by: Mohamed Abbas <mohamed.abbas@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>