[CRYPTO] aes-generic: Make key generation exportable

This patch exports four tables and the set_key() routine. This ressources
can be shared by other AES implementations (aes-x86_64 for instance).
The decryption key has been turned around (deckey[0] is the first piece
of the key instead of deckey[keylen+20]). The encrypt/decrypt functions
are looking now identical (except they are using different tables and
key).

Signed-off-by: Sebastian Siewior <sebastian@breakpoint.cc>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>