dt-bindings: drm/bridge: anx7625: Add aux-bus node

List panel under aux-bus node if it's connected to anx7625's aux bus.

Signed-off-by: Hsin-Yi Wang <hsinyi@chromium.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220213103437.3363848-4-hsinyi@chromium.org