doc: conf: Add 2.4.0 version selector

Adds the 2.4.0 release to the documentation version selector.

Signed-off-by: Maureen Helm <maureen.helm@nxp.com>
diff --git a/doc/conf.py b/doc/conf.py
index d2b17dd..9fff373 100644
--- a/doc/conf.py
+++ b/doc/conf.py
@@ -542,6 +542,7 @@
     'theme_logo_only': False,
     'current_version': version,
     'versions': (("latest", "/"),
+                 ("2.4.0", "/2.4.0/"),
                  ("2.3.0", "/2.3.0/"),
                  ("2.2.0", "/2.2.0/"),
                  ("2.1.0", "/2.1.0/"),