Include configuration file to headers

Add inclusion to configration file in header files,
instead of relying on other header files to include
the configuration file. This issue resolves #1371
diff --git a/ChangeLog b/ChangeLog
index 8eab14b..6cecd5b 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -16,6 +16,11 @@
      programs/pkey/gen_key which previously led to compilation failure
      on some toolchains. Reported by phoenixmcallister. Fixes #2170.
 
+Changes
+   * Include configuration file in all header files that use configuration,
+     instead of relying on other header files that they include.
+     Inserted as an enhancement for #1371
+
 = mbed TLS 2.7.8 branch released 2018-11-30
 
 Security