crypto: drbg - HMAC-SHA1 DRBG has crypto strength of 128 bits

The patch corrects the security strength of the HMAC-SHA1 DRBG to 128
bits. This strength defines the size of the seed required for the DRBG.
Thus, the patch lowers the seeding requirement from 256 bits to 128 bits
for HMAC-SHA1.

Signed-off-by: Stephan Mueller <smueller@chronox.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>