We could run out of space under under 4g, but devices under transparent
bridges can use 64bit resources, so keep trying on the parent bus until
we hit a non-transparent bridge.

Impact: better support for assigning unassigned resources
Reviewed-by: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>