Add the ability to set the ioapic driver using the --features argument:
$ virt-install --features ioapic.driver=qemu ...
This results in the following xml:
<features>
...
<ioapic driver="qemu"/>
</features>
This is required in order to install a guest with >255 cpus. Such a
configuration requires an iommu with extended interrupt mode enabled,
which in turn requires IOMMU interrupt remapping to be enabled, which in
turn requires a split I/O APIC.
Signed-off-by: Jonathon Jongsma <jjongsma@redhat.com>