Change return type of AES decrypt and encrypt

This patch modifies the following 2 functions in the AES module to
change the return type from void to int:
    * mbedtls_aes_encrypt() -> mbedtls_internal_aes_encrypt()
    * mbedtls_aes_decrypt() -> mbedtls_internal_aes_decrypt()
This change is necessary to allow users of MBEDTLS_AES_ALT,
MBEDTLS_AES_DECRYPT_ALT and MBEDTLS_AES_ENCRYPT_ALT to return an error
code when replacing the default with their own implementation, e.g.
a hardware crypto accelerator.
diff --git a/ChangeLog b/ChangeLog
index 4b0c1eb..e02a6ac 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -19,6 +19,14 @@
      suppressing the CA list in Certificate Request messages. The default
      behaviour has not changed, namely every configured CAs name is included.
 
+API Changes
+   * The following functions in the AES module have been deprecated and replaced
+     by the functions shown below. The new functions change the return type from
+     void to int to allow returning error codes when using MBEDTLS_AES_ALT,
+     MBEDTLS_AES_DECRYPT_ALT or MBEDTLS_AES_ENCRYPT_ALT.
+     mbedtls_aes_decrypt() -> mbedtls_internal_aes_decrypt()
+     mbedtls_aes_encrypt() -> mbedtls_internal_aes_encrypt()
+
 Bugfix
    * Remove macros from compat-1.3.h that correspond to deleted items from most
      recent versions of the library. Found by Kyle Keen.