iwlwifi: move show_qos to debugfs

This move the show_qos file from sysfs to debugfs because the "one
value per file" sysfs rule.

The file is located in
/sys/kernel/debug/ieee80211/phy0/iwlagn/data

Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>