drm/msm/dp: replace dp_connector with drm_bridge_connector

There is little point in having both connector and root bridge
implementation in the same driver. Move connector's functionality to the
bridge to let next bridge in chain to override it.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Tested-by: Sankeerth Billakanti <quic_sbillaka@quicinc.com>
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/473854/
Link: https://lore.kernel.org/r/20220211224006.1797846-5-dmitry.baryshkov@linaro.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>