drm/i915: Add vma to list at creation

With the current code there shouldn't be a distinction - however with an
upcoming change we intend to allocate a vma much earlier, before it's
actually bound anywhere.

To do this we have to check node allocation as well for the _bound()
check.

Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
[danvet: move list_del(&vma->vma_link) from vma_unbind to vma_destroy,
again fallout from the loss of "rm/i915: Cleanup more of VMA in
destroy".]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
fixup for drm/i915: Add vma to list at creation