Since we may track unfenced access (GPU access to the vma that
explicitly requires no fence), vma->last_fence may be set without any
attached fence (vma->fence) and so will not be flushed when we call
i915_vma_put_fence(). Since we stopped doing a full retire of the
activity trackers for unbind, we need to explicitly retire each tracker.

Fixes: b0decaf7 ("drm/i915: Track active vma requests")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170620124321.1108-1-chris@chris-wilson.co.ukReviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
(cherry picked from commit 760a898d)
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>