x86/PCI: Use pcibios_scan_root() instead of pci_scan_bus_with_sysdata()

pci_scan_bus_with_sysdata() and pcibios_scan_root() are quite similar:

  pci_scan_bus_with_sysdata
    pci_scan_bus_on_node(..., &pci_root_ops, -1)

  pcibios_scan_root
    pci_scan_bus_on_node(..., &pci_root_ops, get_mp_bus_to_node(busnum))

get_mp_bus_to_node() returns -1 if it couldn't find the node number, so
this removes pci_scan_bus_with_sysdata() and uses pcibios_scan_root()
instead.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>