s390/zcrypt: Introduce cprb mempool for ep11 misc functions

Introduce a cprb mempool for the zcrypt ep11 misc functions
(zcrypt_ep11misc.*) do some preparation rework to support
a do-not-allocate path through some zcrypt ep11 misc functions.

The mempool is controlled by the zcrypt module parameter
"mempool_threshold" which shall control the minimal amount
of memory items for CCA and EP11.

The mempool shall support "mempool_threshold" requests/replies
in parallel which means for EP11 to hold a send and receive
buffer memory per request. Each of this cprb space items is
limited to 8 KB. So by default the mempool consumes
  5 * 2 * 8KB = 80KB

If the mempool is depleted upon one ep11 misc functions is
called with the ZCRYPT_XFLAG_NOMEMALLOC xflag set, the function
will fail with -ENOMEM and the caller is responsible for taking
further actions.

This is only part of an rework to support a new xflag
ZCRYPT_XFLAG_NOMEMALLOC but not yet complete.

Signed-off-by: Harald Freudenberger <freude@linux.ibm.com>
Reviewed-by: Holger Dengler <dengler@linux.ibm.com>
Link: https://lore.kernel.org/r/20250424133619.16495-8-freude@linux.ibm.com
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

Author: hfreude

drivers/s390/crypto/zcrypt_api.c

@@ -2166,6 +2166,10 @@ int __init zcrypt_api_init(void)
 	if (rc)
 		goto out_ccamisc_init_failed;
 
+	rc = zcrypt_ep11misc_init();
+	if (rc)
+		goto out_ep11misc_init_failed;
+
 	/* Register the request sprayer. */
 	rc = misc_register(&zcrypt_misc_device);
 	if (rc < 0)
@@ -2177,6 +2181,8 @@ int __init zcrypt_api_init(void)
 	return 0;
 
 out_misc_register_failed:
+	zcrypt_ep11misc_exit();
+out_ep11misc_init_failed:
 	zcrypt_ccamisc_exit();
 out_ccamisc_init_failed:
 	zcdn_exit();