s390/chsc: cleanup SEI helper functions

Cleanup the functions used to call SEI.
Also provide !CONFIG_PCI dummys for pci error handling.

Reviewed-by: Peter Oberparleiter <peter.oberparleiter@de.ibm.com>
Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>