crypto: acomp - Add ACOMP_REQUEST_ALLOC and acomp_request_alloc_extra

Add ACOMP_REQUEST_ALLOC which is a wrapper around acomp_request_alloc
that falls back to a synchronous stack reqeust if the allocation
fails.

Also add ACOMP_REQUEST_ON_STACK which stores the request on the stack
only.

The request should be freed with acomp_request_free.

Finally add acomp_request_alloc_extra which gives the user extra
memory to use in conjunction with the request.

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