The org.jboss.tools.birt.oda plugin needs to be in the WEB-INF/platform/plugins directory.
If you added this plugin after deploying your web application, you need to start the OSGi runtime with the -clean option at least once.
The easiest way is to remove all files/directories except the config.ini file from the WEB-INF/platform/configuration directory.
The config.ini file has to contain the following:
osgi.bundles=org.eclipse.equinox.common@2\:start, org.eclipse.update.configurator@3\:start, org.eclipse.birt.core@start
osgi.bundles.defaultStartLevel=4
osgi.parentClassloader=fwk
org.osgi.framework.bootdelegation=org.hibernate,org.hibernate.type,org.hibernate.metadata,org.hibernate.ejb, javax.persistence
eclipse.product=org.eclipse.birt.report.engine.ReportEngineSDK