Add hwmon sys I/F for generic thermal driver.

Note: we have one hwmon class device for EACH TYPE of the thermal zone device.
Signed-off-by: NZhang Rui <rui.zhang@intel.com>
Acked-by: NJean Delvare <khali@linux-fr.org>
Signed-off-by: NLen Brown <len.brown@intel.com>