arm64: dts: marvell: uDPU: add missing SoC compatible

According to the bindings, all boards using Armada 37xx SoC-s must have
"marvell,armada3710" compatible while 3720 based ones should also have
"marvell,armada3720" before it.

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>