doc: release notes: Add 2.2 update mbedTLS

Update libraries section with the mbedTLS version

Signed-off-by: Flavio Ceolin <flavio.ceolin@intel.com>
diff --git a/doc/releases/release-notes-2.2.rst b/doc/releases/release-notes-2.2.rst
index db6894c..cdb9152 100644
--- a/doc/releases/release-notes-2.2.rst
+++ b/doc/releases/release-notes-2.2.rst
@@ -641,6 +641,8 @@
     logging from thread context.
   * Improved notification about missing log_strdup.
 
+* mbedTLS updated to 2.16.4
+
 HALs
 ****