Tiva: Add build framework and skeleton files for Tiva I2C driver.  Initial commit is just the STM32 I2C driver with name changes and STM32-specific logic removed

Set the GPIO_SPEED_50MHz on all F2 and F4 SPI pin configurations.  This is based on an F411 SPI1 errata but the fixed is generalized to all SPI and all F2 and F4 (let me know if this introduces any other issues).  Discovered and fixed by Sebastien Lorquet after much consternation.

EFM32 Serial:  Add support for termios TCGET and TCSET.  For the moment, only set/get speed is implemetned.  From Pierre-noel Bouteville