crypto: drbg - header file for DRBG

The header file includes the definition of:

* DRBG data structures with
        - struct drbg_state as main structure
        - struct drbg_core referencing the backend ciphers
        - struct drbg_state_ops callbach handlers for specific code
          supporting the Hash, HMAC, CTR DRBG implementations
        - struct drbg_conc defining a linked list for input data
        - struct drbg_test_data holding the test "entropy" data for CAVS
          testing and testmgr.c
        - struct drbg_gen allowing test data, additional information
          string and personalization string data to be funneled through
          the kernel crypto API -- the DRBG requires additional
          parameters when invoking the reset and random number
          generation requests than intended by the kernel crypto API

* wrapper function to the kernel crypto API functions using struct
  drbg_gen to pass through all data needed for DRBG

* wrapper functions to kernel crypto API functions usable for testing
  code to inject test_data into the DRBG as needed by CAVS testing and
  testmgr.c.

* DRBG flags required for the operation of the DRBG and for selecting
  the particular DRBG type and backend cipher

* getter functions for data from struct drbg_core

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