The adc v2 periph has the same register map, but comes in two flavours, one
supporting injected channels, more watchdogs, per channel sampling times and
so on, and one "simple" version.
Pull up the f3 and f0 portions into the appropriate files, after comparing with
L0 and L4 reference manuals, even if those are not fully landed yet.
The f0, f30x and l0 have a very similar "v2" adc peripheral.
Start extracting out some of the common code, and fix the glaring bug in
adc_power_down that was affecting them both.
This is not intended to be a fully comprehensive extraction, just the first
easy steps.
