Add 2 targets for DISCO_H747I dualcore:
* DISCO_H747I      -> for CM7 core
* DISCO_H747I_CM4  -> for CM4 core

Current restrictions:
* TICKLESS deactivated
* DeepSleep not supported (DeepSleep wrapped to sleep)

Warning: use of the same IP (example I2C1) by both core at the same time is not prevented,
but is strongly not recommended.
Some Hardware Semaphore are use for common IP, to manage concurrent access by both cores: Flash, GPIO, RCC.

Warning: Drag and drop of binary to DISCO_H747I will flash CM7.
         In order to flash CM4, one can use STM32 CubeProgrammer tool.