[Utopic][Pull] pci support for arm64

[Dann Frazier]

I've prepared a backport of the patches from linux-next to enable PCI on arm64:
    git://kernel.ubuntu.com/dannf/ubuntu-utopic-hyperscale.git arm64-pci

I've successfully tested this with the latest xgene-pcie driver
submission and verified that a plug-in NIC card works.

Though this pull request doesn't enable any hardware by itself, my
goal is to get it merged now since it touches core code and find any
regressions before the upcoming freeze. Once this is in, the changes
needed to add PCI support for a new platform should be much more
localized.