drm/bridge_connector: implement oob_hotplug_event

Implement the oob_hotplug_event() callback. Translate it to the HPD
notification sent to the HPD bridge in the chain.

Reviewed-by: Janne Grunau <j@jannau.net>
Link: https://lore.kernel.org/r/20231009174048.2695981-4-dmitry.baryshkov@linaro.org


Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20231009174048.2695981-4-dmitry.baryshkov@linaro.org