drm/msm/dp: migrate the ycbcr_420_allowed to drm_bridge

drm/msm/dp: migrate the ycbcr_420_allowed to drm_bridge

Instead of forcing the ycbcr_420_allowed flag to be set on the created
drm_connector, set it on the drm_bridge instance and allow
drm_bridge_connecgtor to propagate it to the drm_connector.

Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Acked-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Reviewed-by: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20241019-bridge-yuv420-v1-5-d74efac9e4e6@linaro.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>