drm/msm/dpu: drop ununused PINGPONG features

All existing PINGPONG feature bits are completely unused. Drop them from
the current codebase.

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/655409/
Link: https://lore.kernel.org/r/20250522-dpu-drop-features-v5-28-3b2085a07884@oss.qualcomm.com