crypto: x86/sha256_ssse3 - move SHA-224/256 SSSE3 implementation to base layer

This removes all the boilerplate from the existing implementation,
and replaces it with calls into the base layer. It also changes the
prototypes of the core asm functions to be compatible with the base
prototype

  void (sha256_block_fn)(struct sha256_state *sst, u8 const *src, int blocks)

so that they can be passed to the base layer directly.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>