This is a follow-on to 'vPCI: avoid bogus "overlap in extended cap list"
warnings', addressing further issues noted there.

1: PCI: determine whether a device has extended config space
2: PCI: pass pdev to pci_ats_{device,enabled}()
3: x86/MSI: pass pdev to read_pci_mem_bar()
4: PCI: pass pdev to pci_find_{,next_}ext_capability()
5: PCI: don't look for ext-caps when there's no extended cfg space
6: vPCI/DomU: really no ext-caps without extended config space

Jan