pci_ari_enabled() is useful outside of drivers/pci, particularly for
deriving INTx routing via ACPI _PRT, so move it to the global header.
Also convert to bool return.
Signed-off-by: Alex Williamson <alex.williamson@redhat.com> Signed-off-by: Bjorn Helgaas <bhelgaas@google.com> Reviewed-by: Don Dutile <ddutile@redhat.com> Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>