s390/pci: implement pcibios_add_device

Use pcibios_add_device to do arch specific device initialization.
This function will be called during pci_bus_add_device.

Reviewed-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>