hwmon: (adt7475) Voltage attenuators can be bypassed

It is possible to bypass the voltage attenuators on the +2.5V, Vccp,
+5V and +12V voltage monitoring inputs. This is useful to connect
other voltage channels than the ones the monitoring chip was
originally designed for. When this feature is enabled, we must not
include the scaling factors in our computations.

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>