s390/kvm: Interrupt injection bugfix

EXTERNAL_CALL and EMERGENCY type interrupts need to preserve their interrupt
code parameter when being injected from user space.

Signed-off-by: Jason J. Herne <jjherne@us.ibm.com>
Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>