s390/zcrypt: CCA control CPRB sending

s390/zcrypt: CCA control CPRB sending

When sending a CCA CPRB to a control domain, the CPRB has to be sent via a
usage domain.  Previous code used the default domain to route this message.
If the default domain is not online and ready to send the CPRB, the ioctl will
fail even if other usage domains could be used to send the CPRB.

To improve this, instead of using the default domain, switch to auto-select of
the domain.

Signed-off-by: Juergen Christ <jchrist@linux.ibm.com>
Reviewed-by: Harald Freudenberger <freude@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>