crypto: testmgr - fuzz skciphers against their generic implementation

When the extra crypto self-tests are enabled, test each skcipher
algorithm against its generic implementation when one is available.
This involves: checking the algorithm properties for consistency, then
randomly generating test vectors using the generic implementation and
running them against the implementation under test.  Both good and bad
inputs are tested.

This has already detected a bug in the skcipher_walk API, a bug in the
LRW template, and an inconsistency in the cts implementations.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>