Update the documentation for the thermal driver hwmon sys I/F.

Change the ACPI thermal zone type to be consistent with hwmon.
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>