As suggested by Eric for the Blake2b implementation contributed by
David, introduce a set of test vectors for Blake2s covering different
digest and key sizes.

          blake2s-128  blake2s-160  blake2s-224  blake2s-256
         ---------------------------------------------------
len=0   | klen=0       klen=1       klen=16      klen=32
len=1   | klen=16      klen=32      klen=0       klen=1
len=7   | klen=32      klen=0       klen=1       klen=16
len=15  | klen=1       klen=16      klen=32      klen=0
len=64  | klen=0       klen=1       klen=16      klen=32
len=247 | klen=16      klen=32      klen=0       klen=1
len=256 | klen=32      klen=0       klen=1       klen=16

Cc: David Sterba <dsterba@suse.com>
Cc: Eric Biggers <ebiggers@google.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>