KVM: s390: clarify kvm related kernel message

As suggested by our ID dept. here are some kernel message
updates.

Signed-off-by: Michael Mueller <mimu@linux.ibm.com>
Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>