vfio-plugin: refactor and fix bugs in enumeration

[r-rojo]

• Refactor enumeration in vfio plugin to match PCIe attributes (BDF, socket id)
  • Add functions, pci_matches_filters and pci_matches_filter that are called first during enumeration.
    • If the filters are empty or the the pci attributes in the filters match the device, it is considered for the rest of enumeration
    • Otherwise, it is skipped
  • Move token lists from a static token list into the static list of pci_device_t structures.
  • This helps prevent reading of CSR space by filtering on specific PCIe attributes read from sysfs
    IOW, given a specific PCIe address (segment, bus, device, function), the mmio space will be read only when the PCIe address is
    set in the filter and it matches a device.
• Fix use of open_vfio_pair so that it is called only when a VF has a PF
  physfn AND that device is bound to the vfio-pci driver.
• Read afu_id for BAR0 when treating a whole device as an accelerator.

[coveralls]

Coverage decreased (-0.007%) to 75.361% when pulling 2224392 on rrojo/vfio_plugin_refactor_enum into 86282f4 on master.

[tswhison]

s/;;/;/ :)