This commit completes the do_pci_info() conversion to
QObject by adding support to PCI bridge devices.

This is done by recursively adding devices in the
"pci_bridge" key.

IMPORTANT: This code is being added separately because I could
NOT test it properly. According to Michael Tsirkin, it depends
on ultrasparc and it would take time to do the proper setup.
Signed-off-by: NLuiz Capitulino <lcapitulino@redhat.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>