Allow to forward declare of public structs #1215

Thanks to forward declare we can declare `struct` in our header file instead making #include
diff --git a/include/mbedtls/ccm.h b/include/mbedtls/ccm.h
index 5d727e7..e1dc124 100644
--- a/include/mbedtls/ccm.h
+++ b/include/mbedtls/ccm.h
@@ -68,7 +68,8 @@
  * \brief    The CCM context-type definition. The CCM context is passed
  *           to the APIs called.
  */
-typedef struct {
+typedef struct mbedtls_ccm_context
+{
     mbedtls_cipher_context_t cipher_ctx;    /*!< The cipher context used. */
 }
 mbedtls_ccm_context;