dt-bindings: display/msm: dp-controller: document QCS8300 compatible

dt-bindings: display/msm: dp-controller: document QCS8300 compatible

Add compatible string for the DisplayPort controller found on the
Qualcomm QCS8300 SoC.

The Qualcomm QCS8300 platform comes with one DisplayPort controller
that supports 4 MST streams, similar to the one found on the SA8775P.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Yongxing Mou <yongxing.mou@oss.qualcomm.com>
Patchwork: https://patchwork.freedesktop.org/patch/684200/
Link: https://lore.kernel.org/r/20251029-qcs8300_mdss-v13-2-e8c8c4f82da2@oss.qualcomm.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>