drm/syncobj: disable the timeline UAPI for now v2

Until we have sorted out all problems.

v2: return -EINVAL during create if flag is set.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/260937/