crypto: x86/sha256 - autoload if SHA-NI detected

The x86 SHA-256 module contains four implementations: SSSE3, AVX, AVX2,
and SHA-NI.  Commit 1c43c0f1 ("crypto: x86/sha - load modules based
on CPU features") made the module be autoloaded when SSSE3, AVX, or AVX2
is detected.  The omission of SHA-NI appears to be an oversight, perhaps
because of the outdated file-level comment.  This patch fixes this,
though in practice this makes no difference because SSSE3 is a subset of
the other three features anyway.  Indeed, sha256_ni_transform() executes
SSSE3 instructions such as pshufb.

Reviewed-by: Roxana Nicolescu <roxana.nicolescu@canonical.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>