[S390] ap: Setup processing for messages in request queue.

Setup timer for processing messages in request queue, if sending an AP
message returns with reason code AP_RESPONSE_RESET_IN_PROGRESS.

Signed-off-by: Holger Dengler <hd@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>