arm: stm32: add new architecture for STM32MP family

- add new arch stm32mp for STM32 MPU/Soc based on Cortex A
- support for stm32mp157 SOC
- SPL is used as first boot stage loader
- using driver model for all the drivers, even in SPL
- all security feature are deactivated (ETZC and TZC)
- reused STM32 MCU drivers when it is possible

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>