ARM: dts: stm32: Add STM32H743 MCU and STM32H743i-EVAL board

Add basic support for STM32H743 MCU and his eval board.
The STMicrolectornics's STM32H743 MCU is based on  Cortex-M7 core
running up to @400MHz with 2MB internal flash and 1MB internal RAM.

For more details see:
Documentation/arm/stm32/stm32h743-overview.txt

Signed-off-by: Alexandre TORGUE <alexandre.torgue@st.com>