iwlwifi: Thermal Throttling debugfs function

Add debugfs function to display current thermal throttling status for
both Legacy and Advance Thermal Throttling Management

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>