crypto: doc - Add explicit title heading to API docs

Documentation for crypto programming interfaces lack explicit title.
As such, all its sections become entries in the toctree index.

Add the title heading to tidy up toctree.

Signed-off-by: Bagas Sanjaya <bagasdotme@gmail.com>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Tested-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Documentation/crypto/api-aead.rst

@@ -1,3 +1,6 @@
+Authenticated Encryption With Associated Data (AEAD)
+====================================================
+
 Authenticated Encryption With Associated Data (AEAD) Algorithm Definitions
 --------------------------------------------------------------------------
 

Documentation/crypto/api-akcipher.rst

@@ -1,3 +1,6 @@
+Asymmetric Cipher
+=================
+
 Asymmetric Cipher Algorithm Definitions
 ---------------------------------------
 

Documentation/crypto/api-digest.rst

@@ -1,3 +1,6 @@
+Message Digest
+==============
+
 Message Digest Algorithm Definitions
 ------------------------------------
 

Documentation/crypto/api-kpp.rst

@@ -1,3 +1,6 @@
+Key-agreement Protocol Primitives (KPP)
+=======================================
+
 Key-agreement Protocol Primitives (KPP) Cipher Algorithm Definitions
 --------------------------------------------------------------------
 

Documentation/crypto/api-rng.rst

@@ -1,3 +1,6 @@
+Random Number Generator (RNG)
+=============================
+
 Random Number Algorithm Definitions
 -----------------------------------
 

Documentation/crypto/api-sig.rst

@@ -1,3 +1,6 @@
+Asymmetric Signature
+====================
+
 Asymmetric Signature Algorithm Definitions
 ------------------------------------------
 

Documentation/crypto/api-skcipher.rst

@@ -1,3 +1,6 @@
+Symmetric Key Cipher
+====================
+
 Block Cipher Algorithm Definitions
 ----------------------------------