This patch implements a new method by which hw_random hardware drivers
can pass data to the core more efficiently, using a shared buffer.

The old methods have been retained as a compatability layer until all the
drivers have been updated.
Signed-off-by: NIan Molton <ian.molton@collabora.co.uk>
Acked-by: NMatt Mackall <mpm@selenic.com>
Acked-by: NRusty Russell <rusty@rustcorp.com.au>
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>