In many places, we wish to store the VMA in preference to the object
itself and so being able to create the persistent VMA is useful.
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/1471254551-25805-9-git-send-email-chris@chris-wilson.co.uk