PCI: Inline the ATS setup code into pci_ats_init()

The ATS setup code in ats_alloc_one() is only used by pci_ats_init(), so
inline it there.  No functional change.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Joerg Roedel <jroedel@suse.de>