drm/amd/display: Add support for programming stereo sync

Signed-off-by: Vitaly Prosyak <vitaly.prosyak@amd.com>
Acked-by: Harry Wentland <Harry.Wentland@amd.com>
Reviewed-by: Charlene Liu <Charlene.Liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>