crypto: powerpc - Stress test for vpmsum implementations

vpmsum implementations often don't kick in for short test vectors.
This is a simple test module that does a configurable number of
random tests, each up to 64kB and each with random offsets.

Both CRC-T10DIF and CRC32C are tested.

Cc: Anton Blanchard <anton@samba.org>
Signed-off-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>