crypto: drbg - Convert to new rng interface

crypto: drbg - Convert to new rng interface

Orabug: 27926676
CVE: CVE-2017-15116

This patch converts the DRBG implementation to the new low-level
rng interface.

This allows us to get rid of struct drbg_gen by using the new RNG
API instead.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Acked-by: Stephan Mueller <smueller@chronox.de>
(cherry picked from commit 8fded5925d0a733c46f8d0b5edd1c9b315882b1d)
Signed-off-by: Brian Maly <brian.maly@oracle.com>
Conflicts:
	crypto/drbg.c

Signed-off-by: Brian Maly <brian.maly@oracle.com>