Support of linux kernel training on stm32mp1

[cmadianga]

This PR adds all needed to support the stm32mp1 board for the linux kernel training.

[github-actions]

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[cmadianga]

I have read the CLA Document and I hereby sign the CLA.

[tpetazzoni]

Thanks @cmadianga for your contribution! We are just wondering whether this is something we want to merge, not because the contribution isn't good, but because we're not really planning on extending coverage for the STM32MP1 platform in our training courses, and rather to switch to other more modern platforms. So merging this PR would cause additional maintenance effort on our side (to test/validate our kernel training on STM32MP1 and keep it regularly up-to-date), but no really benefit.

[cmadianga]

Thanks @tpetazzoni for your feedback. I understand your point of view.
For your information, I also have the same work done for STM32MP2.
If you are interested please let me know.