If you want to use myfaces you will need to bundle it with your application, however it will not be integrated with the container, so things like injection into JSF managed beans will not work.
In order to figure out what the actual problem is with your deployment you will need a later version of JBoss AS7. You can get a pre-release version of final that has this bug fixed from:
https://github.com/jbossas/jboss-as/zipball/7.0.0.Final-prerelease