Up until a while ago, libvirt would automatically add a legacy
PCI controllers combo (dmi-to-pci-bridge + pci-bridge) to any
PCIe machine type (x86_64/q35 and aarch64/virt).
As a result, a number of input and output files in the test
suite ended up containing the legacy PCI controllers, even
though they are not needed or in any way relevant to the
feature being tested.
Get rid of most of the occurrences. Most of the time, this
just means removing the controllers from the input file and
regenerating the output files; in a few instances, some
minor tweaking is performed on the input file, most notably
removing the memory balloon: as memory balloon support was
not the scope of the test being changed, there is no loss
of test coverage from doing so.
Several occurrences of the legacy PCI controllers remain in
the test suite, both because removing their usage would have
required even more tweaking, and because we still want to
have coverage of this perfectly valid combination.
This controller provides a single PCIe port on a new root. It is
similar to pci-expander-bus, intended to provide a bus that can be
associated with a guest-identifiable NUMA node, but is for
machinetypes with PCIe rather than PCI (e.g. q35-based machinetypes).
Aside from PCIe vs. PCI, the other main difference is that a
pci-expander-bus has a companion pci-bridge that is automatically
attached along with it, but pcie-expander-bus has only a single port,
and that port will only connect to a pcie-root-port, or to a
pcie-switch-upstream-port. In order for the bus to be of any use in
the guest, it must have either a pcie-root-port or a
pcie-switch-upstream-port attached (and one or more
pcie-switch-downstream-ports attached to the
pcie-switch-upstream-port).
