crypto: skcipher - make chunksize and walksize accessors internal

The 'chunksize' and 'walksize' properties of skcipher algorithms are
implementation details that users of the skcipher API should not be
looking at.  So move their accessor functions from <crypto/skcipher.h>
to <crypto/internal/skcipher.h>.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>