s390/crypto: Postpone the key split to key conversion

s390/crypto: Postpone the key split to key conversion

Store the input key material of paes-xts in a single key_blob
structure. The split of the input key material is postponed to the key
conversion. Split the key material only, if the returned protected
keytype requires a second protected key.

For clear key pairs, prepare a clearkey token for each key and convert
them separately to protected keys. Store the concatenated conversion
results as input key in the context. All other input keys are stored
as is.

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