s390/pkey: Support new xflag PKEY_XFLAG_NOCLEARKEY

s390/pkey: Support new xflag PKEY_XFLAG_NOCLEARKEY

Introduce a new xflag PKEY_XFLAG_NOCLEARKEY which when given refuses
the conversion of "clear key tokens" to protected key material.

Some algorithms (PAES, PHMAC) have the need to construct "clear key
tokens" to be used during selftest. But in general these algorithms
should only support clear key material for testing purpose. So now the
algorithm implementation can signal via xflag PKEY_XFLAG_NOCLEARKEY
that a conversion of clear key material to protected key is not
acceptable and thus the pkey layer (usually one of the handler
modules) refuses clear key material with -EINVAL.

Signed-off-by: Harald Freudenberger <freude@linux.ibm.com>
Reviewed-by: Holger Dengler <dengler@linux.ibm.com>
Reviewed-by: Ingo Franzki <ifranzki@linux.ibm.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>