Add support for all U5 ADCs

[klownfish]

This merge request adds register definitions for all ADCs on the U5 series. Currently only ADC4 is supported.

The reason for this is that not all ADCs on the U5 are of the same version. Some are similar to V4 (ADC1/2), while others are closer to V3 (ADC4). To work around this I have prefixed everything related to ADC4 and instantiated both versions as blocks in adc_u5.yaml. This approach seemed to produce the cleanest results when implementing the driver in embassy.

I refer to ADC4 explicitly everywhere which might seem questionable but I believe it’s the best approach. It has been a constant pattern throughout the U5 series and given how the modules are numbered (1, 2, and 4) I think it's clear that 4 is the outlier.

First draft of the embassy driver:
https://github.com/klownfish/embassy/tree/u5_adc/embassy-stm32/src/adc

related issue:
#522

[embassy-ci]

diff: https://ci.embassy.dev/jobs/1889b04d5be2/artifacts/diff.html

[MDr164]

Looks good to me. I'll give it a try in conjunction with your updated ADC driver for the U5 series this week.

[embassy-ci]

diff: https://ci.embassy.dev/jobs/657a12b9b8ac/artifacts/diff.html

[MDr164]

I tested the updated metapac and the driver you created in your fork using different voltage on all the defined ADC variants and they all worked correctly! @klownfish would you mind opening a PR on the embassy repo for discussion on the new ADC driver you created to make use of the updated ADC definitions?