hwmon: (via-cputemp) Add VID reporting support

At least VIA family 6 model D CPU report the VID settings in a MSR,
so expose the value to user-space. Not sure about model A.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Acked-by: Guenter Roeck <guenter.roeck@ericsson.com>
Tested-by: Jeff Rickman <jrickman@myamigos.us>