Change self test for AES_CGM to perform both an encrypt and decrypt.

Change self test for AES_CGM to perform both an encrypt and decrypt.

This is a request from the lab that changes the AES_GCM test back to perform both a encrypt and
decrypt. (This makes no logical sense since this is not an inverse cipher).
I have left the AES_ECB decrypt test in (although it may not be needed)
since it is actually testing the inverse cipher case.

Reviewed-by: Tim Hudson <tjh@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/15844)