dt-bindings: arm: stm32: Add Engicam i.Core STM32MP1 EDIMM2.2 Starter Kit

i.Core STM32MP1 is an EDIMM SoM based on STM32MP157A from Engicam.

EDIMM2.2 Starter Kit is an EDIMM 2.2 Form Factor Capacitive Evaluation
Board from Engicam.

i.Core STM32MP1 needs to mount on top of this Evaluation board for
creating complete i.Core STM32MP1 EDIMM2.2 Starter Kit.

Add bindings for it.

Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>