s390/pkey/crypto: Introduce xflags param for pkey in-kernel API

Add a new parameter xflags to the in-kernel API function
pkey_key2protkey(). Currently there is only one flag supported:

* PKEY_XFLAG_NOMEMALLOC:
  If this flag is given in the xflags parameter, the pkey
  implementation is not allowed to allocate memory but instead should
  fall back to use preallocated memory or simple fail with -ENOMEM.
  This flag is for protected key derive within a cipher or similar
  which must not allocate memory which would cause io operations - see
  also the CRYPTO_ALG_ALLOCATES_MEMORY flag in crypto.h.

The one and only user of this in-kernel API - the skcipher
implementations PAES in paes_s390.c set this flag upon request
to derive a protected key from the given raw key material.

Signed-off-by: Harald Freudenberger <freude@linux.ibm.com>
Reviewed-by: Holger Dengler <dengler@linux.ibm.com>
Link: https://lore.kernel.org/r/20250424133619.16495-26-freude@linux.ibm.com


Signed-off-by: Heiko Carstens <hca@linux.ibm.com>