thermal: add hwmon sysfs I/F

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: Zhang Rui <rui.zhang@intel.com>
Acked-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Len Brown <len.brown@intel.com>