xen/pcifront: Deprecate pci_get_bus_and_slot()

pci_get_bus_and_slot() is restrictive such that it assumes domain=0 as
where a PCI device is present. This restricts the device drivers to be
reused for other domain numbers.

Use pci_get_domain_bus_and_slot() with a domain number of 0 where we can't
extract the domain number. Other places, use the actual domain number from
the device.

Signed-off-by: Sinan Kaya <okaya@codeaurora.org>
Signed-off-by: Bjorn Helgaas <helgaas@kernel.org>
Reviewed-by: Juergen Gross <jgross@suse.com>