[S390] zcrypt: Fix possible dead lock in AP bus module.

If a AP device is unconfigured __ap_poll_all() will call
device_unregister() in software interrupt context which can cause
dead locks. To fix this the device will be only marked as unconfigured
and the device_unregister() call will be done later by either
ap_scan_bus() or ap_queue_message() in process context.

Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Ralph Wuerthner <rwuerthn@de.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>