pciehp: fix slot name

Current pciehp uses the combination of bus number and slot number as a
slot name. But it is not a good idea because bus number is not a
physical identifier but a logical identifier. This is against the PCIE
specification. So remove the bus number from the physical identifier.

However, there are some platforms with the problem that it provides
the same slot number. For those platforms, this patch also introduces
new module option 'pciehp_slot_with_bus'. If it is specified, pciehp
uses the combination of bus number and slot number as a slot name.

Signed-off-by: Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>
Signed-off-by: Kristen Carlson Accardi <kristen.c.accardi@intel.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>