s390/pci: use pdev->dev.groups for attribute creation

Let the driver core handle attribute creation by putting all s390
specific pci attributes in an attribute group which is referenced
by pdev->dev.groups in pcibios_add_device.

Link: https://lkml.kernel.org/r/alpine.LFD.2.11.1404141101500.1529@denkbrett


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>