Add support for MultiTech mDot module

Module is based around an STM32F405RG processor.  Let me know if I'm missing anything.
Done.  There were 2 platforms that used GCC_ARM, so I thought it would be OK.  They are DISCO_F334C8 and DISCO_F429ZI, though I note they only list support for GCC_ARM.  Is this restriction documented anywhere?