s390/pci: s390 specific PCI sysfs attributes

Add some s390 specific sysfs attributes to the PCI device directory.
The following attributes are introduced:
- function_id (PCI function ID)
- function_handle (PCI function handle)
- pchid (PCI channel ID)
- pfgid (PCI function group ID aka PCI root complex)

Signed-off-by: Jan Glauber <jang@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>