crypto: export arc4 defines

Some arc4 cipher algorithm defines show up in two places:
crypto/arc4.c and drivers/crypto/bcm/cipher.h.
Let's export them in a common header and update their users.

Signed-off-by: Iuliana Prodan <iuliana.prodan@nxp.com>
Reviewed-by: Horia Geantă <horia.geanta@nxp.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>