staging/android: remove .{fence, timeline}_value_str() from timeline_ops

Now that the value of fence and the timeline are not stored by sw_sync
anymore we can remove this extra abstraction to retrieve this data.

This patch changes both fence_ops (.fence_value_str and
.timeline_value_str) to return the str directly.

It also clean up struct sync_timeline_ops by removing both ops from there.

Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Sumit Semwal <sumit.semwal@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>