drm/bridge: parade-ps8640: Populate devices on aux-bus

Conventionally, panel is listed under the root of the device tree.
When userland asks for display mode, ps8640 bridge is responsible
for returning EDID when ps8640_bridge_get_edid() is called.

Now enable a new option of listing panel under "aux-bus" of ps8640
bridge node in the device tree. In this case, panel driver can retrieve
EDID by triggering AUX transactions, without ps8640_bridge_get_edid()
calls at all.

To prevent the "old" and "new" options from interfering with each
other's logic flow, disable DRM_BRIDGE_OP_EDID when the new option
is taken.

Signed-off-by: Philip Chen <philipchen@chromium.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20211028105754.v5.2.I09899dea340f11feab97d719cb4b62bef3179e4b@changeid