lspci: Print buses of multibus PCI domain in ascending order

lspci: Print buses of multibus PCI domain in ascending order

Currently PCI domains are printed in ascending order. Devices on each PCI
bus are also printed in ascending order. PCI buses behind PCI-to-PCI
bridges are also printed in ascending order.

But buses of PCI domain are currently printed in descending order because
function new_bus() puts newly created bus at the beginning of linked list.

In most cases PCI domain contains only one (top level) bus, so in most
cases it is not visible this inconsistency.

Multibus PCI domains (where PCI domain contains more independent top level
PCI buses) are available on ARM devices.

This change fixes print order of multibus PCI domains, so also top level
PCI buses are printed in ascending order, like PCI buses behind PCI-to-PCI
bridges.