115200 is a much more sane "default" than 38400.
Instead of a mix of 38400 and 115200, just use 115200 in all places.
There's no reason for modern 32bit cpus to be using such old slow
baudrates.
Tested on f1, f4, l1. Replaced some old f1 code that predated some
library support code for this.
This brings in the new ADC api for STM32 parts.
Update to new standardized ADC apis.
Drops pointless channel definitions, uses common names for common functions.
No functional changes.
Based on work in: https://github.com/libopencm3/libopencm3-examples/pull/130
