arm64: dts: sdm845: Add dispcc node

This adds the display clock controller node to sdm845 based on the
examples in the bindings.

Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>