crypto: testmgr - add gcm(aes) decryption tests to encryption tests

Some "gcm(aes)" decryption test vectors don't exactly match any of the
encryption test vectors with input and result swapped.  In preparation
for removing the AEAD decryption test vectors and testing AEAD
decryption using the encryption test vectors, add these to the
encryption test vectors, so we don't lose any test coverage.

In the case of the chunked test vector, I truncated the last scatterlist
element to the end of the plaintext.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>