hwmon: (w83791d) add support for thermal cruise mode

Add support to set target temperature and tolerance for thermal
cruise mode.

Signed-off-by: Marc Hulsman <m.hulsman@tudelft.nl>
Acked-by: Hans de Goede <j.w.r.degoede@hhs.nl>
Signed-off-by: Jean Delvare <khali@linux-fr.org>