drm/msm/dpu: rework static color fill code

Rework static color fill code to separate the pipe / pipe_cfg handling.
This is a preparation for the r_pipe support.

Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Tested-by: Abhinav Kumar <quic_abhinavk@quicinc.com> # sc7280
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/527340/
Link: https://lore.kernel.org/r/20230316161653.4106395-26-dmitry.baryshkov@linaro.org


Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>