dt-bindings: display/msm: qcom, sc8280xp-mdss: add DP / eDP child nodes

Describe DP and eDP devices as subdevices to the MDSS on SC8280XP
platform.

Fixes: 45af56bf ("dt-bindings: display/msm: Add binding for SC8280XP MDSS")
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Acked-by: Rob Herring <robh@kernel.org>
Patchwork: https://patchwork.freedesktop.org/patch/518799/
Link: https://lore.kernel.org/r/20230118031718.1714861-2-dmitry.baryshkov@linaro.org


Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>