[S390] cio: Cleanup crw interface.

Eliminate the need for the machine check handler to call into
the common I/O layer directly by introducing an interface to
register handlers for crws per rsc.

Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>