drm/msm/dpu: use dpu_sw_pipe for dpu_hw_sspp callbacks

Where feasible, use dpu_sw_pipe rather than a combo of dpu_hw_sspp and
multirect_index/_mode arguments.

Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>