drm/msm/dpu: use single CTL if it is the only CTL returned by RM

On DPU >= 5.0 CTL blocks were reworked in order to support using a
single CTL for all outputs. In preparation of reworking the RM code to
return single CTL make sure that dpu_encoder can cope with that.

Reviewed-by: Marijn Suijten <marijn.suijten@somainline.org>
Tested-by: Neil Armstrong <neil.armstrong@linaro.org> # on SM8550-QRD
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Jessica Zhang <quic_jesszhan@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/641582/
Link: https://lore.kernel.org/r/20250307-dpu-active-ctl-v3-4-5d20655f10ca@linaro.org


Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>