arm64: dts: qcom: sc7180-trogdor: Move panel under the bridge chip

Putting the panel under the bridge chip (under the aux-bus node)
allows the panel driver to get access to the DP AUX bus, enabling all
sorts of fabulous new features.

While we're at this, get rid of a level of hierarchy for the panel
node. It doesn't need "ports / port" and can just have a "port" child.

For Linux, this patch has a hard requirement on the patches adding DP
AUX bus support to the ti-sn65dsi86 bridge chip driver. See the patch
("drm/bridge: ti-sn65dsi86: Add support for the DP AUX bus").

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20210611101711.v10.11.Ibdb7735fb1844561b902252215a69526a14f9abd@changeid