drm/msm/dpu: Refactor sc7280_pp location

The sc7280_pp declaration is not located by the other _pp
declarations, but rather hidden around the _merge_3d
declarations. Let's fix this to avoid confusion.

Signed-off-by: Robert Foss <robert.foss@linaro.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/509153/
Link: https://lore.kernel.org/r/20221028120812.339100-3-robert.foss@linaro.org


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