Besides C files for the BSP variant the patch also provides license
clarification on system_stm32h7xx.c file which is provided
in boards/stm/stm32h747i-disco directory.
The files comes from STM32CubeH7 project and references "root directory"
in its license comment and it's not clear where this points out.
Let's add clarification comment about it and also based on it
and resulting license let's add SPDX license identifier.
Sponsored-By: Precidata
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