drm/msm: remove unused plane_property field from msm_drm_private

drm/msm: remove unused plane_property field from msm_drm_private

Remove unused field plane_property from struct msm_drm_private. Also
drop the enum msm_mdp_plane_property which also becomes unused.

Fixes: 7d36db0be3b9 ("drm/msm/mdp5: switch to standard zpos property")
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Patchwork: https://patchwork.freedesktop.org/patch/480939/
Link: https://lore.kernel.org/r/20220406100556.479706-1-dmitry.baryshkov@linaro.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>