PCI: Move ATS declarations in seperate header file

This patch moves the relevant declarations from the local
header file in drivers/pci to a more accessible locations so
that it can be used by the AMD IOMMU driver too.
The file is named pci-ats.h because support for the PCI PRI
capability will also be added there in a later patch-set.

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Acked-by: Jesse Barnes <jbarnes@virtuousgeek.org>