KVM: s390: refactor interrupt delivery code

Move delivery code for cpu-local interrupt from the huge do_deliver_interrupt()
to smaller functions which handle one type of interrupt.

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