crypto: caam/rng - Add support for PRNG

Add support for random number generation using PRNG
mode of CAAM and expose the interface through crypto API.

According to the RM, the HW implementation of the DRBG follows
NIST SP 800-90A specification for DRBG_Hash SHA-256 function

Signed-off-by: Meenakshi Aggarwal <meenakshi.aggarwal@nxp.com>
Reviewed-by: Horia Geant <horia.geanta@nxp.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>