s390/ap: add error response code field for ap queue devices

On AP instruction failures the last response code is now
kept in the struct ap_queue. There is also a new sysfs
attribute showing this field (enabled only on debug kernels).

Also slight rework of the AP_DBF macros to get some more
content into one debug feature message line.

Signed-off-by: Harald Freudenberger <freude@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>