PCI: xgene: Request host bridge window resources

Request host bridge window resources so they appear in ioport_resource and
iomem_resource and are reflected in /proc/ioports and /proc/iomem.

For example, the following entries did not previously appear in /proc/iomem:

  e180000000-e1ffffffff : /soc/pcie@1f2b0000
    e180000000-e182ffffff : PCI Bus 0000:01
      e180000000-e181ffffff : 0000:01:00.0
      e182000000-e1820fffff : 0000:01:00.0
      e182100000-e1821fffff : 0000:01:00.0
  f000000000-ffffffffff : /soc/pcie@1f2b0000

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>