dt-bindings: display: msm: dp-controller: document SM8450 compatible

The SM8450 & SM350 shares the same DT TX IP version, use the
SM8350 compatible as fallback for SM8450.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/527564/
Link: https://lore.kernel.org/r/20230206-topic-sm8450-upstream-dp-controller-v6-1-d78313cbc41d@linaro.org


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