arm64: dts: qcom: sc8180x: add empty mdss_edp_out endpoint

arm64: dts: qcom: sc8180x: add empty mdss_edp_out endpoint

Follow the example of other DP controllers and also eDP controller on
SC7280 and move mdss_edp_out endpoint declaration to the SoC DTSI. This
slightly reduces the boilerplate in the platform DT files and also
reduces the difference between DP and eDP controllers.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Reviewed-by: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>
Link: https://lore.kernel.org/r/20250724-move-edp-endpoints-v1-1-6ca569812838@oss.qualcomm.com
Signed-off-by: Bjorn Andersson <andersson@kernel.org>