iwlwifi: mvm: add debugfs to force CT-kill

CT-kill is a thermal-based "RF-kill", which disables the NIC
completely if the temperature gets too high, in order to avoid damage.

Add a debugfs entry to simulate high temperatures, in order to test
CT-kill flows in the driver without having to physically heat the
device up.

Signed-off-by: Chaya Rachel Ivgi <chaya.rachel.ivgi@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>