Add a bare bones framework that will do nothing more than support configuration for the Atmel SAMV71 Xplained Ultra board.  Very much a work in progress.

Fix two uses of DEBUG_COLORATION vs STACK_COLORATION (from David Sidrane).  Also some corrected comments

PIC32MZ SPI:  Implement exchange() method; update SPI_REGDEBUG configuration and clean up implementation

Adds architecture support for the STM32F372 and F373 (no board support yet). Only tested on STM32F373CC, but should work on the rest.  Contributed by  Marten Svanfeldt.