drm/panel-edp: use put_sync in unprepare

Some edp panel requires T10 (Delay from end of valid video data transmitted
by the Source device to power-off) less than 500ms. Using autosuspend with
delay set as 1000 violates this requirement.

Use put_sync_suspend in unprepare to meet the spec. For other cases (such
as getting EDID), it still uses autosuspend.

Suggested-by: Douglas Anderson <dianders@chromium.org>
Fixes: 3235b0f2 ("drm/panel: panel-simple: Use runtime pm to avoid excessive unprepare / prepare")
Signed-off-by: Hsin-Yi Wang <hsinyi@chromium.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20231220221418.2610185-1-hsinyi@chromium.org