s390/ap: re-enable interrupt for AP queues

This patch introduces some code lines which check
for interrupt support enabled on an AP queue after
a reply has been received. This invocation has been
chosen as there is a good chance to have the queue
empty at that time. As the enablement of the irq
imples a state machine change the queue should not
have any pending requests or unreceived replies.

Reviewed-by: Tony Krowiak <akrowiak@linux.ibm.com>
Reviewed-by: Holger Dengler <dengler@linux.ibm.com>
Signed-off-by: Harald Freudenberger <freude@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>