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.
Be specifically careful with the usb examples. There is likely some
breakage to be expected, not sure I updated all the drivers to the
correct types for the respective chips.
