drm/msm/dsi: remove the drm_bridge_attach fallback

All the bridges that are being used with the MSM DSI hosts have been
converted to support DRM_BRIDGE_ATTACH_NO_CONNECTOR. Drop the fallback
code and require DRM_BRIDGE_ATTACH_NO_CONNECTOR to be supported by the
downstream bridges.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/582209/
Link: https://lore.kernel.org/r/20240309-fd-dsi-cleanup-bridges-v1-1-962ebdba82ed@linaro.org