sensors: grove_light: convert to devicetree bindings

Replace Kconfig configuration data with devicetree bindings using
(ADC) io channels.  Rework the sample to document expectations about
the relationship between the reference voltage and the divider input
voltage, and update the sensor configuration to support Nordic SAADC.

Signed-off-by: Peter Bigot <peter.bigot@nordicsemi.no>
8 files changed