s390/chsc: query utility strings via fmt3 channel path descriptor

Add support for format 3 channel path descriptors and use them to
gather utility strings.

Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Reviewed-by: Peter Oberparleiter <oberpar@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>