drm/msm/dpu: don't use merge_3d if DSC merge topology is used

DPU supports different topologies for the case when multiple INTFs are
being driven by the single phys_enc. The driver defaults to using 3DMux
in such cases. Don't use it if DSC merge is used instead.

Suggested-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Vinod Koul <vkoul@kernel.org>
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/480922/
Link: https://lore.kernel.org/r/20220406094031.1027376-9-vkoul@kernel.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>