drm/msm/mdp5: use drm atomic helpers to handle base drm plane state

Use generic helpers code to manage drm_plane_state part of mdp5_plane
state instead of manually coding all the details.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://lore.kernel.org/r/20210525131316.3117809-2-dmitry.baryshkov@linaro.org


Signed-off-by: Rob Clark <robdclark@chromium.org>