drm_bridge: register content protect property

Some bridges can update HDCP status based on userspace requests if they
support HDCP.

The HDCP property is created after connector initialization and before
registration, just like other connector properties.

Add the content protection property to the connector if a bridge
supports HDCP.

Signed-off-by: Hsin-Yi Wang <hsinyi@chromium.org>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Fei Shao <fshao@chromium.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Link: https://lore.kernel.org/r/20250812082135.3351172-2-fshao@chromium.org