This reverts commit ecebca79.

Do not enable fence callback on poll() when using fence_array causes the
fence_array to not signal.

For now we will revert the change and enable signaling everytime time
poll is called with timeout=0 as well.

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NGustavo Padovan <gustavo.padovan@collabora.co.uk>
Acked-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1479457603-30758-1-git-send-email-gustavo@padovan.org