s390/zcrypt: add ap_adapter_mask sysfs attribute

This patch provides a new sysfs attribute file
/sys/bus/ap/ap_adapter_mask. This read-only attribute
refrects the apm field as it is found in the PQAP(QCI)
crypto info.

Signed-off-by: Harald Freudenberger <freude@linux.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>