dt-bindings: display: msm-dsi-controller-main: document the SM8650 DSI Controller

Document the DSI Controller on the SM8650 Platform.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/564972/
Link: https://lore.kernel.org/r/20231030-topic-sm8650-upstream-mdss-v2-2-43f1887c82b8@linaro.org


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