Instead of implemeting zpos property on our own, use standard zpos
property support.
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://lore.kernel.org/r/20210525131316.3117809-6-dmitry.baryshkov@linaro.orgSigned-off-by: Rob Clark <robdclark@chromium.org>