CA-46050: allow more than 2 PCI devices to be hotplugged into a domain (!)

CA-46050: allow more than 2 PCI devices to be hotplugged into a domain (!)

There is much confusion about the meaning of the X in
(X, (domain, bus, path, func)). Sometimes it means "order the device was
plugged"; other times it means something more device related.

With this change, more than 2 devices can be plugged into a domain and the
#devices and plug order remains constant over reboot.

Signed-off-by: David Scott <dave.scott@eu.citrix.com>