Introduce MBEDTLS_SSL_NULL_CIPHERSUITES

The support for TLS ciphersuites without
encryption does not rely anymore on the
MBEDTLS_CIPHER_NULL_CIPHER feature of
the cipher module. Introduce a specific
config option to enable these ciphersuites
and use it instead of MBEDTLS_CIPHER_NULL_CIPHER.

Signed-off-by: Ronald Cron <ronald.cron@arm.com>
diff --git a/ChangeLog.d/mbedtls-ssl-null-ciphersuites.txt b/ChangeLog.d/mbedtls-ssl-null-ciphersuites.txt
new file mode 100644
index 0000000..a1312d0
--- /dev/null
+++ b/ChangeLog.d/mbedtls-ssl-null-ciphersuites.txt
@@ -0,0 +1,4 @@
+API changes
+   * Add MBEDTLS_SSL_NULL_CIPHERSUITES configuration option. It enables
+     TLS 1.2 ciphersuites without encryption and is disabled by default.
+     This new option replaces MBEDTLS_CIPHER_NULL_CIPHER.