arm64: dts: qcom: ipq8074: add SoC specific compatible to MDIO

Add the newly documented SoC compatible to MDIO in order to be able to
validate clocks for it.

Signed-off-by: Robert Marko <robimarko@gmail.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20221114194734.3287854-5-robimarko@gmail.com