Assorted analog-related simplifications/clean up

[jessebraham]

Just some small changes, cleaning things up a bit. Part of my prelude-simplification-yak-shaving adventure (more fun to come!).

• Remove the analog modules from the chip-specific HAL packages
  • Not sure why these existed in the first place? Historical reasons? Regardless, not necessary
• Merge the SarAdcExt and SensExt traits into a single AnalogExt trait
  • There was no reason for these to be different traits
• A bit of clean up and simplification in the analog module

[bjoernQ]

LGTM 👍