I'm really not happy that we have to support this, but this will be the
simplest way to handle cases where PPGTT init can fail, which I promise
will be coming in the future.

v2: Resolve conflicts due to patch series reordering.

Signed-off-by: Ben Widawsky <ben@bwidawsk.net> (v1)
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>