drm/bridge: tc358767: fix output H/V syncs

The H and V syncs of the DP output are always set to active high. This
patch fixes the syncs by configuring them according to the videomode.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Reviewed-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190103115954.12785-7-tomi.valkeinen@ti.com