powerpc/pci: Don't unset PCI resources for VFs

Flag PCI_REASSIGN_ALL_RSRC is used to ignore resources information setup by
firmware, so that kernel would re-assign all resources of pci devices.

On powerpc arch, this happens in a header fixup function
pcibios_fixup_resources(), which will clean up the resources if this flag
is set. This works fine for PFs, since after clean up, kernel will
re-assign the resources in pcibios_resource_survey().

Below is a simple call flow on how it works:

    pcibios_init
      pcibios_scan_phb
        pci_scan_child_bus
          ...
            pci_device_add
              pci_fixup_device(pci_fixup_header)
                pcibios_fixup_resources                     # header fixup
                  for (i = 0; i < DEVICE_COUNT_RESOURCE; i++)
                    dev->resource[i].start = 0
      pcibios_resource_survey                               # re-assign
        pcibios_allocate_resources

However, the VF resources won't be re-assigned, since the VF resources are
completely determined by the PF resources, and the PF resources have
already been reassigned. This means we need to leave VF's resources
un-cleared in pcibios_fixup_resources().

In this patch, we skip the resource unset process in
pcibios_fixup_resources(), if the pci_dev is a VF.

Signed-off-by: Wei Yang <weiyang@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>