Merge branch 'pci/enumeration'

- Split out ARI "next function" handling from the traditional one (Niklas
  Schnelle)

- Move jailhouse "isolated function" (non-zero functions where function 0
  doesn't exist) handling to pci_scan_slot() to avoid duplicating
  multi-function scanning in pci_scan_child_bus_extend() (Niklas Schnelle)

- Extend "isolated function" probing to s390 (Niklas Schnelle).

- Allow s390 zPCI zbus without a function 0 (Niklas Schnelle)

* pci/enumeration:
  s390/pci: allow zPCI zbus without a function zero
  PCI: Extend isolated function probing to s390
  PCI: Move jailhouse's isolated function handling to pci_scan_slot()
  PCI: Split out next_ari_fn() from next_fn()
  PCI: Clean up pci_scan_slot()