drm/i915: Double check activity before relocations

If the object is active and we need to perform a relocation upon it, we
need to take the slow relocation path. Before we do, double check the
active requests to see if they have completed.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1470293567-10811-22-git-send-email-chris@chris-wilson.co.uk