s390/zcrypt: support for extended number of ap domains

Extends the number of ap domains within the zcrypt device driver up to 256.
AP domains in the range 00..255 will be detected.

Signed-off-by: Ingo Tuchscherer <ingo.tuchscherer@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>