drm/msm/dpu: enable PINGPONG TE operations only when supported by HW

drm/msm/dpu: enable PINGPONG TE operations only when supported by HW

The DPU_PINGPONG_TE bit is set for all PINGPONG blocks on DPU < 5.0.
Rather than checking for the flag, check for the presense of the
corresponding interrupt line.

Reviewed-by: Marijn Suijten <marijn.suijten@somainline.org>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/555541/
Link: https://lore.kernel.org/r/20230904020454.2945667-3-dmitry.baryshkov@linaro.org