[S390] cio: use ccw request infrastructure for pgid

Use the newly introduced ccw request infrastructure to implement
pgid related operations: sense pgid, set pgid and disband pg.

Signed-off-by: Peter Oberparleiter <peter.oberparleiter@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>