s390/pci: add exception table to load/store instructions

Don't let pci_load and friends crash the kernel when called with
e.g. an invalid offset. Return -ENXIO instead.

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>