dt-bindings: display: msm: dp: declare compatible string for sm8150

Add compatible string for the DisplayPort controller found on the
Qualcomm SM8150 platform.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/571438/
Link: https://lore.kernel.org/r/20231209232132.3580045-2-dmitry.baryshkov@linaro.org