ath11k: add thermal cooling device support

Thermal cooling device support is added to control the temperature by
throttling the data transmission for the given duration. Throttling is
done by suspending all data tx queues by given percentage of time. The
thermal device allows user to configure duty cycle.

Throttling can be disabled by setting the duty cycle to 0. The cooling
device can be found under /sys/class/thermal/cooling_deviceX/.
Corresponding soft link to this device can be found under phy folder.

/sys/class/ieee80211/phy*/device/cooling_device.

To set duty cycle as 40%,

echo 40 >/sys/class/ieee80211/phy*/device/cooling_device/cur_state

Signed-off-by: Pradeep Kumar Chitrapu <pradeepc@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>