Have you taken a look at the schema? It looks like it has the same elements so it should be rather straightforward to create jboss-ejb3.xml using your existing jboss.xml as a starting point.
Here's the jboss-ejb3.xml Reference.
NOTE: I think the schemaLocation is not correct in the reference. It uses http://www.jboss.org/j2ee/schema/jboss-ejb3-2_0.xsd, which does not exist. The correct schema location is http://xmlns.jcp.org/xml/ns/javaee/ejb-jar_3_2.xsd. I just created a discussion in the Wildfly group about the schema location problem.
You don't mention where your jboss.xml is located so for completeness just a reminder that for Wildfly it should be in WEB-INF of a war, or META-INF of an EJB jar.