drm/msm/dpu: fix blend setup for DMA4 and DMA5 layers

SM8550 uses new register to map SSPP_DMA4 and SSPP_DMA5 units to blend
stages. Add proper support for this register to allow using these two
planes for image processing.

Fixes: efcd0107

 ("drm/msm/dpu: add support for SM8550")
Cc: Neil Armstrong <neil.armstrong@linaro.org>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Tested-by: Neil Armstrong <neil.armstrong@linaro.org> # on SM8550
Patchwork: https://patchwork.freedesktop.org/patch/518481/
Link: https://lore.kernel.org/r/20230116063316.728496-1-dmitry.baryshkov@linaro.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>