IOMMU group creation for pseries hotplug, and powernv VFs

[Oliver O'Halloran]

A couple of extra patches on top of Shawn's existing re-ordering patch.
This seems to fix the problem Alexey noted with Shawn's change causing
VFs to lose their IOMMU group. I've tried pretty hard to make this a
minimal fix it's still a bit large.

If mpe is happy to take this as a fix for 5.4 then I'll leave it,
otherwise we might want to look at different approaches.