qemu: fix qemuDomainSupportsPCI() for ARM machines of "virt" machinetype

qemu: fix qemuDomainSupportsPCI() for ARM machines of "virt" machinetype

Commit e8d5517 updated the domain post-parse to automatically add
pcie-root et al for certain ARM "virt" machinetypes, but didn't update
the function qemuDomainSupportsPCI() which is called later on when we
are auto-assigning PCI addresses and default settings for the PCI
controller <model> and <target> attributes. The result was that PCI
addresses weren't assigned, and the controllers didn't have their
attribute default values set, leading to an error when the domain was
started, e.g.:

  internal error: autogenerated dmi-to-pci-bridge options not set

This patch adds the same check made in the earlier patch to
qemuDomainSupportsPCI(), so that PCI address auto-assignment and
target/model default values will be set.