Add support for mDot with STM32F411RE processor

@bcostm I need to support the STM32F411RE for mDot, but I'm unsure where you are at with simplifying the ST targets.  This largely duplicates the Nucleo F411RE.  I'm adding this pull request to create a talking point.  If you don't mind this being pulled now and simplified later, great.  If not, just let me know a timeline on your work.