dt-bindings: display/msm: sm8150-mdss: add DP node

As Qualcomm SM8150 got support for the DisplayPort, add displayport@
node as a valid child to the MDSS node.

Fixes: 88806318

 ("dt-bindings: display: msm: dp: declare compatible string for sm8150")
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/586156/
Link: https://lore.kernel.org/r/20240402-fd-fix-schema-v3-1-817ea6ddf775@linaro.org
Signed-off-by: Abhinav Kumar <quic_abhinavk@quicinc.com>