drm/msm/dpu: drop now-unused condition for has_legacy_ctls

drm/msm/dpu: drop now-unused condition for has_legacy_ctls

Now as we have dropped the DPU_CTL_SPLIT_DISPLAY from DPU >= 5.0
configuration, drop the rm->has_legacy_ctl condition which short-cutted
the check for those platforms.

Suggested-by: Marijn Suijten <marijn.suijten@somainline.org>
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>
Patchwork: https://patchwork.freedesktop.org/patch/641586/
Link: https://lore.kernel.org/r/20250307-dpu-active-ctl-v3-8-5d20655f10ca@linaro.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>