[CRYPTO] api: Add crypto_ablkcipher_ctx_aligned

This is function does the same thing for ablkcipher that is done for
blkcipher by crypto_blkcipher_ctx_aligned(): it returns an aligned
address of the private ctx.

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