docs(auth): add auth_decrypt in CM chapter

The call to REGISTER_CRYPTO_LIB requires auth_decrypt function to be
provided. Add its prototype and update REGISTER_CRYPTO_LIB call.

Signed-off-by: Yann Gautier <yann.gautier@foss.st.com>
Change-Id: Id1f2a54867ffe5dec36e0bf22490d01858891585
diff --git a/docs/design/auth-framework.rst b/docs/design/auth-framework.rst
index 38a1173..508a82f 100644
--- a/docs/design/auth-framework.rst
+++ b/docs/design/auth-framework.rst
@@ -241,6 +241,11 @@
                      unsigned char output[CRYPTO_MD_MAX_SIZE])
     int (*verify_hash)(void *data_ptr, unsigned int data_len,
                        void *digest_info_ptr, unsigned int digest_info_len);
+    int (*auth_decrypt)(enum crypto_dec_algo dec_algo, void *data_ptr,
+                        size_t len, const void *key, unsigned int key_len,
+                        unsigned int key_flags, const void *iv,
+                        unsigned int iv_len, const void *tag,
+                        unsigned int tag_len);
 
 These functions are registered in the CM using the macro:
 
@@ -250,7 +255,8 @@
                         _init,
                         _verify_signature,
                         _calc_hash,
-                        _verify_hash);
+                        _verify_hash,
+                        _auth_decrypt);
 
 ``_name`` must be a string containing the name of the CL. This name is used for
 debugging purposes.