Depending if the qemu binary supports multiple pci-busses, the device
options will contain "bus=pci" or "bus=pci.0".

Only x86_64 and i686 seem to have support for multiple PCI-busses. When
a guest of these architectures is started, set the
QEMUD_CMD_FLAG_PCI_MULTIBUS flag.
Signed-off-by: NNiels de Vos <ndevos@redhat.com>