s390/zcrypt: remove VLA usage from the AP bus

The use of variable length arrays on the stack is deprecated.
git commit 3d8f60d3
"s390/zcrypt: hex string mask improvements for apmask and aqmask."
added three new VLA arrays. Remove them again.

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