It was always expected to have a use for this some day, so we left a
placeholder.  Now we do.  (And I expect another use in the not too
distant future when we start allowing userspace to allocate GPU iova.)
Signed-off-by: Rob Clark <robdclark@chromium.org>
Link: https://lore.kernel.org/r/20220304005317.776110-3-robdclark@gmail.com