Allow AES XTS decryption using duplicate keys.

This feature is enabled by default outside of FIPS builds
which ban such actions completely.

Encryption is always disallowed and will generate an error.

Reviewed-by: Tomas Mraz <tmraz@fedoraproject.org>
(Merged from https://github.com/openssl/openssl/pull/9112)

(cherry picked from commit 2c840201e57e27fa9f1b26a970270a91813e32fe)