hwmon: (adt7475) Add VID support for the ADT7476

The ADT7476 has 5 dedicated pins for VID input, and the +12V input can
optionally be used as a 6th VID pin. Add support for VID input.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Cc: Hans de Goede <hdegoede@redhat.com>
Cc: Jordan Crouse <jordan@cosmicpenguin.net>
Cc: "Darrick J. Wong" <djwong@us.ibm.com>