ARM: dts: qcom: ipq4018-ap120c-ac: setup serial console

Add the required alias and stdout property so that kernel can setup
the console based off DTS and not have to set it in the cmdline.

Signed-off-by: Robert Marko <robert.marko@sartura.hr>
Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230214161211.306462-1-robert.marko@sartura.hr