1004: Fix internal channels for adc v2 r=lulf a=chemicstry
Internal channel reading was broken on adc_v2, because `Adc::read()` requires gpio pin trait, which was not implemented by `VrefInt`, `Temperature`, `Vbat`. The required configuration bits `tsvrefe`, `vbate` were not enabled either. This PR makes it a bit closer to how adc_v4 works.
While at it, I also changed adc_v2 to use `RccPeripheral` instead of permanently enabling all ADCs.
Co-authored-by: chemicstry <chemicstry@gmail.com>
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