s390/zcrypt: Rework domain processing within zcrypt device driver

s390/zcrypt: Rework domain processing within zcrypt device driver

Slight rework of the domain handling within the zcrypt dd:
Remove this curious construct to give a pointer to the
domain field within the CPRB struct to the zcrypt API and
later fill in the target domain via this pointer.
Now the domain is filled in with the send function when
the ready constructed AP message is about to be pushed
down into the software queue for AP queue processing.
So now the domain handling for CCA, EP11 and (internal) rng
CPRBs is the same. With this comes a slight reshuffle of the
code related to domain processing in the zcrypt API and the
message type 60 protocol implementation code.

Reviewed-by: Holger Dengler <dengler@linux.ibm.com>
Signed-off-by: Harald Freudenberger <freude@linux.ibm.com>
Acked-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>