drm/msm/dpu: get rid of DPU_PINGPONG_DSC

drm/msm/dpu: get rid of DPU_PINGPONG_DSC

Continue migration to the MDSS-revision based checks and replace
DPU_PINGPONG_DSC feature bit with the core_major_ver < 7 check.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Patchwork: https://patchwork.freedesktop.org/patch/655390/
Link: https://lore.kernel.org/r/20250522-dpu-drop-features-v5-16-3b2085a07884@oss.qualcomm.com