arm64: PCI: Allow resource reallocation if necessary

Call pci_assign_unassigned_root_bus_resources() instead of the simpler:

  pci_bus_size_bridges(bus);
  pci_bus_assign_resources(bus);

pci_assign_unassigned_root_bus_resources() calls:

  __pci_bus_size_bridges(bus, add_list);
  __pci_bus_assign_resources(bus, add_list, &fail_head);

so this should be equivalent as long as we're able to assign everything.
If we were unable to assign something, previously we did nothing and left
it unassigned, but after this patch, we will attempt to do some
reallocation.

Once we start honoring FW resource allocations, this will bring up the
"reallocation" feature which can help making room for SR-IOV when
necessary.

Link: https://lore.kernel.org/r/20190615002359.29577-1-benh@kernel.crashing.org


Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
[bhelgaas: commit log]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>