DTS property attributes are (by default) not required.
Explicitly specifying `required: false` is redundant.
Perhaps a warning to that effect would be useful.
Signed-off-by: Chris Friedt <cfriedt@meta.com>
Define RaspberryPi Pico ADC.
The ADC has internally connected temperature sensor,
Add property to enable this.
The ADC has a single VREF. VCC usually connects to it,
but it may not be in a case.
Add property to make configurable it.
Signed-off-by: TOKITA Hiroshi <tokita.hiroshi@fujitsu.com>