crypto: hash - Add request chaining API

crypto: hash - Add request chaining API

This adds request chaining to the ahash interface.  Request chaining
allows multiple requests to be submitted in one shot.  An algorithm
can elect to receive chained requests by setting the flag
CRYPTO_ALG_REQ_CHAIN.  If this bit is not set, the API will break
up chained requests and submit them one-by-one.

A new err field is added to struct crypto_async_request to record
the return value for each individual request.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>