This commit is based upon prior work of @dpgeorge and @koendv.

MCU support for the STM32H7A3 and B3 families MCUs:
- STM32H7A3xx
- STM32H7A3xxQ (SMPS)
- STM32H7B3xx
- STM32H7B3xxQ (SMPS)

Support has been added for the STM32H7B3I_DK board.
Signed-off-by: NJan Staal <info@janstaal.com>