PCI, PCI Hotplug: introduce slot_name helpers

In preparation for cleaning up the various hotplug drivers
such that they don't have to manage their own 'name' parameters
anymore, we provide the following convenience functions:

	pci_slot_name()
	hotplug_slot_name()

These helpers will be used by individual hotplug drivers.

Cc: kristen.c.accardi@intel.com
Cc: matthew@wil.cx
Acked-by: Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>
Signed-off-by: Alex Chiang <achiang@hp.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>