drm/i915: Use common LRU inactive vma bumping for unpin_from_display

Now that i915_gem_object_bump_inactive_ggtt() exists, also make use of
it for the LRU bumping from i915_gem_object_unpin_from_display()

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/20170119192659.31789-2-chris@chris-wilson.co.uk


Reviewed-by: Jonas Lahtinen <joonas.lahtinen@linux.intel.com>