crypto: arc4 - now arc needs blockcipher support

Since commit ce6dd368 ("crypto: arc4 - improve performance by adding
ecb(arc4)) we need to pull in a blkcipher.

|ERROR: "crypto_blkcipher_type" [crypto/arc4.ko] undefined!
|ERROR: "blkcipher_walk_done" [crypto/arc4.ko] undefined!
|ERROR: "blkcipher_walk_virt" [crypto/arc4.ko] undefined!

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