s390/pfault: do not use stack buffers for hardware data

With CONFIG_VMAP_STACK=y the stack is allocated from the vmalloc space.
Data structures passed to a hardware or a hypervisor interface that
requires V=R can not be allocated on the stack anymore.

Make the init and fini pfault parameter blocks static variables.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>