[S390] cio: Kerneldoc comments for cmf.

- Fix existing kerneldoc-style comments.
- Move descriptions of functions from cmb.h to cmf.c.

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>