drm/msm/dpu: do not limit the zpos property

Stop limiting zpos property values, we use normalized_zpos anyway. And
nothing stops userspace from assigning several planes to a single zpos
(it is a userspace bug, but the kernel is forgiving about it).

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/473147/
Link: https://lore.kernel.org/r/20220209172520.3719906-3-dmitry.baryshkov@linaro.org


Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>