arm64: dts: sc7180: Support Parade ps8640 edp bridge

Add a dts fragment file to support the sc7180 boards with the second
source edp bridge, Parade ps8640.

Signed-off-by: Philip Chen <philipchen@chromium.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20211008113839.v3.2.I187502fa747bc01a1c624ccf20d985fdffe9c320@changeid