PCI: Convert pci_info() to QObject

PCI: Convert pci_info() to QObject

The returned QObject is a QList of all buses. Each bus is
represented by a QDict, which has a key with a QList of all
PCI devices attached to it. Each device is represented by
a QDict.

As has happended to other complex conversions, it's hard to
split this commit as part of it are new functions which are
called by each other.

IMPORTANT: support for printing PCI bridge attached devices
is NOT part of this commit, it's going to be added by the
next commit, as it's untested.

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>