iwlwifi: move channels sysfs to debugfs

This patch moves channels info display from sysfs to debugfs.
This shows channel information as stored in NIC EEPROM. This
is useful in debugging CRDA or iwl goes setting so it belongs
rather to debugfs then to sysfs.

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