drm/msm/dpu: add dpu_plane_atomic_print_state

drm/msm/dpu: add dpu_plane_atomic_print_state

Implement plane's atomic_print_state() callback, printing DPU-specific
plane state: blending stage, SSPP and multirect mode and index.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Link: https://lore.kernel.org/r/20211215160912.2715956-2-dmitry.baryshkov@linaro.org
[DB: marked pdpu and pstate as const]
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>