s390/zcrypt: move ap_msg param one level up the call chain

Move the creating and disposal of the struct ap_message one
level up the call chain. The ap message was constructed in the
calling functions in msgtype50 and msgtype6 but only for the
ica rsa messages. For CCA and EP11 CPRBs the ap message struct
is created in the zcrypt api functions.

This patch moves the construction of the ap message struct into
the functions zcrypt_rsa_modexpo and zcrypt_rsa_crt. So now all
the 4 zcrypt api functions zcrypt_rsa_modexpo, zcrypt_rsa_crt,
zcrypt_send_cprb and zcrypt_send_ep11_cprb appear and act
similar.

There are no functional changes coming with this patch.
However, the availability of the ap_message struct has
advantages which will be needed by a follow up patch.

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