crypto: drbg - Add select on sha256

The hash-based DRBG variants all use sha256 so we need to add a
select on it.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/Kconfig

@@ -1508,10 +1508,11 @@ config CRYPTO_DRBG_HMAC
 	bool
 	default y
 	select CRYPTO_HMAC
+	select CRYPTO_SHA256
 
 config CRYPTO_DRBG_HASH
 	bool "Enable Hash DRBG"
-	select CRYPTO_HASH
+	select CRYPTO_SHA256
 	help
 	  Enable the Hash DRBG variant as defined in NIST SP800-90A.