dt-bindings: marvell: armada-37xx: add Methode eDPU compatible

Document compatible for the Methode eDPU Armada 3720 based board.

Signed-off-by: Robert Marko <robert.marko@sartura.hr>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>