s390/crypto: fix gcm-aes-s390 selftest failures

The current kernel uses improved crypto selftests. These
tests showed that the current implementation of gcm-aes-s390
is not able to deal with chunks of output buffers which are
not a multiple of 16 bytes. This patch introduces a rework
of the gcm aes s390 scatter walk handling which now is able
to handle any input and output scatter list chunk sizes
correctly.

Code has been verified by the crypto selftests, the tcrypt
kernel module and additional tests ran via the af_alg interface.

Cc: <stable@vger.kernel.org>
Reported-by: Julian Wiedmann <jwi@linux.ibm.com>
Reviewed-by: Patrick Steuer <steuer@linux.ibm.com>
Signed-off-by: Harald Freudenberger <freude@linux.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>