altos/telefire*: Do voltage tests in decivolts instead of ADC units

altos/telefire*: Do voltage tests in decivolts instead of ADC units

This requires that each pad device specify the ADC reference voltage
and all relevant voltage divider resistor values explicitly so that
the ADC values can be converted to decivolts and compared with one
another. This should be easier to understand in the future when
reading the code.

Signed-off-by: Keith Packard <keithp@keithp.com>