I have resolved this - it was my misunderstanding of JBOSS 7 - thanks to @jgitter for help.
I had assumed JSF support was being added but found that adding this to the jboss-deployment-structure.xml file allowed it to be deployed OK. Still not sure if its needed in both places.
<deployment>
<dependencies>
<module name="javax.faces.api" slot="main"/>
<module name="com.sun.jsf-impl" slot="main"/>
</dependencies>
</deployment>
<sub-deployment name="myWebApp.war">
<dependencies>
<module name="javax.faces.api" slot="main"/>
<module name="com.sun.jsf-impl" slot="main"/>
</dependencies>
</sub-deployment>