ARM: dts: stm32: Add Engicam MicroGEA STM32MP1 SoM

MicroGEA STM32MP1 is a STM32MP157A based Micro SoM.

General features:
- STM32MP157AAC
- Up to 1GB DDR3L-800
- 512MB Nand flash
- I2S

MicroGEA STM32MP1 needs to mount on top of Engicam MicroDev carrier
boards for creating complete platform solutions.

Add support for it.

Signed-off-by: Matteo Lisi <matteo.lisi@engicam.com>
Signed-off-by: Francesco Utel <francesco.utel@engicam.com>
Signed-off-by: Mirko Ardinghi <mirko.ardinghi@engicam.com>
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>