iwlagn: move sysfs files to debugfs

The debug_level and temperature files should be in
debugfs, the txpower file is completely unneeded
since TX power can be set with iw/iwconfig.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>