Add BSP for STM32H7

Original author: sebastian.huber

Add a BSP for the STM32H7 series. Import the HAL from https://github.com/STMicroelectronics/stm32h7xx_hal_driver. Add a VERSION file to allow future updates similar to https://git.rtems.org/rtems/tree/cpukit/dtc/VERSION. Add standard clock and console drivers.