drm/msm/dpu: split dpu_plane_atomic_check()

Split dpu_plane_atomic_check() function into two pieces:

dpu_plane_atomic_check_nosspp() performing generic checks on the pstate,
without touching the associated SSPP blocks,

and

dpu_plane_atomic_check_sspp(), which takes into account used SSPPs.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/621484/
Link: https://lore.kernel.org/r/20241025-dpu-virtual-wide-v6-5-0310fd519765@linaro.org