drm/msm/dpu: allow sharing SSPP between planes

drm/msm/dpu: allow sharing SSPP between planes

Since SmartDMA planes provide two rectangles, it is possible to use them
to drive two different DRM planes, first plane getting the rect_0,
another one using rect_1 of the same SSPP. The sharing algorithm is
pretty simple, it requires that each of the planes can be driven by the
single rectangle and only consecutive planes are considered.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/650441/
Link: https://lore.kernel.org/r/20250426-dpu-share-sspp-v7-1-6f4c719e373c@oss.qualcomm.com
Reviewed-by: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>