The default DRBG is the one that has the highest priority. The priority
is defined based on the order of the list drbg_cores[] where the highest
priority is given to the last entry by drbg_fill_array.

With this patch the default DRBG is switched from HMAC SHA256 to HMAC
SHA512 to support compliance with SP800-90B and SP800-90C (current
draft).

The user of the crypto API is completely unaffected by the change.
Signed-off-by: Stephan Mueller <smueller@chronox.de>
Acked-by: simo Sorce <simo@redhat.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>