dt-bindings: arm: Add Data Modul i.MX8M Plus eDM SBC

Add DT compatible for Data Modul i.MX8M Plus eDM SBC board.
This is an evaluation board for various custom display units.

Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Marek Vasut <marex@denx.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>