feat(docs): introduce STM32MP2 doc

STM32MP2x is a new family of microprocessors designed by
STMicroelectronics and based on Arm Cortex-A35.

Signed-off-by: Yann Gautier <yann.gautier@foss.st.com>
Change-Id: I741ed0a701a614817a4d0b65d3d6f4e6a79da6a9
3 files changed