ia64/PCI: SN: convert to pci_scan_root_bus() for correct root bus resources

Convert from pci_scan_bus() to pci_scan_root_bus().  Supply the root
bus resources from bussoft.  When we move the resource adjustment from
pcibios_fixup_resources() to the PCI core, it will be important to have
the root bus resources correct from the beginning.

CC: Tony Luck <tony.luck@intel.com>
CC: Jack Steiner <steiner@sgi.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>