With Ram's fixes, this should be safe to do again.  So let's give it
another try.

BIOS separates IO ranges between several IOHs, and on some slots, BIOS
assigns resources to a bridge, but stops assigning resources to the
device under that bridge, because the device needs a big resource.

So:
1. allocate resources and record the failed device resources
2. clear the BIOS assigned resources of the parent bridge of failing device
3. go back and call pci assign unassigned
4. if it still fails, go up the tree, clear more bridges. and try again

Now Ram's allocate requested resource already got into mainline. could
put this one again.
Reviewed-by: Ram Pai <linuxram@us.ibm.com>
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>