Initial DMA support for STM32H7
arch/arm/src/stm32h7: SPI DMA mode
arch/arm/src/stm32h7/chip/stm32h7x3xx_memorymap.h: add base addresses for D1, D2 and D3 domain; use 2 bytes to specify memory region
arch/arm/src/stm32h7/stm32h7x3xx_rcc.c: add D1 domain core prescaler configuration
Approved-by: Gregory Nutt <gnutt@nuttx.org>