thermal: update the documentation

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