frv/PCI: convert to pci_scan_root_bus() for correct root bus resources
Convert from pci_scan_bus() to pci_scan_root_bus() and remove root bus
resource fixups. This fixes the problem of "early" and "header" quirks
seeing incorrect root bus resources.
Note that peer root buses are scanned with pci_scan_bus() (which is now
deprecated), so they have the default ioport_resource and iomem_resource
resources. This is unchanged from before, but these resources are
incorrect, and I don't know how to discover the correct ones.