drm/msm/dpu: add dpu_hw_pipe_cfg to dpu_plane_state

Now as all accesses to pipe_cfg and pstate have been cleaned, re-add
struct dpu_hw_pipe_cfg back to dpu_plane_state, so that
dpu_plane_atomic_check() and dpu_plane_atomic_update() do not have a
chance to disagree about src/dst rectangles (currently
dpu_plane_atomic_check() uses unclipped rectangles, while
dpu_plane_atomic_update() uses clipped rectangles calculated by
drm_atomic_helper_check_plane_state()).

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>