drm/bridge: adv7511: make it honour next bridge in DT

DT bindings for adv7511 and adv7533 bridges specify HDMI output to be
present at the port@1. This allows board DT to add e.g. HDMI connector
nodes or any other next chained bridge. Make adv7511 driver discover
that bridge and attach it to the chain.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://lore.kernel.org/r/20240331-adv7511-next-bridge-v2-1-7356d61dc7b2@linaro.org
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240331-adv7511-next-bridge-v2-1-7356d61dc7b2@linaro.org