KVM: s390: sigp: inject emergency calls in a separate function

In preparation for further code changes, this patch moves the injection of
emergency calls into a separate function and uses it for the processing of
SIGP EMERGENCY CALL and SIGP CONDITIONAL EMERGENCY CALL.

Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Acked-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>