Add support for mr76006 pre-scaler which provides divide-by-2 scaling
of the input voltage, so that it can be  presented to the VM for
measurement within its range (the VM input range is limited from -0.1V
to 1V).

The driver reads from the device-tree all the channels that use the
mr76006 pre-scaler and multiplies the voltage result by a factor of 2,
to represent to the user with the actual voltage input source.

Channels that are not in the device-tree are multiplied by a factor
of 1.
Signed-off-by: Eliav Farber <farbere@amazon.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20220908152449.35457-15-farbere@amazon.com
[groeck: Addressed conflicts against commit d59eacaa]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>