drm/msm/dpu: rework vsync_source handling

The struct msm_display_info has is_te_using_watchdog_timer field which
is neither set anywhere nor is flexible enough to specify different
sources. Replace it with the field specifying the vsync source using
enum dpu_vsync_source.

Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Marijn Suijten <marijn.suijten@somainline.org>
Patchwork: https://patchwork.freedesktop.org/patch/598738/
Link: https://lore.kernel.org/r/20240613-dpu-handle-te-signal-v2-5-67a0116b5366@linaro.org