arm64: dts: sc7180: Factor out ti-sn65dsi86 support

Factor out ti-sn65dsi86 edp bridge as a separate dts fragment.
This helps us introduce the second source edp bridge later.

Signed-off-by: Philip Chen <philipchen@chromium.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Doug Anderson <dianders@chromium.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20211008113839.v3.1.Ibada67e75d2982157e64164f1d11715d46cdc42c@changeid