PCI: Export pci_ats_disabled() as a GPL symbol to modules

Building drivers for ATS-aware IOMMUs as modules requires access to
pci_ats_disabled(). Export it as a GPL symbol to get things working.

Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Will Deacon <will@kernel.org>
Tested-by: John Garry <john.garry@huawei.com> # smmu v3
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Joerg Roedel <jroedel@suse.de>