GeoServer does not come built-in with support for Postgis raster columns, it must be installed through an extension. Proceed to Image Mosaic JDBC for installation details. This extension includes the support for Postgis raster.
Adding an Postgis raster data store¶
Read the geotools documentation for Postgis raster Support: http://docs.geotools.org/latest/userguide/library/coverage/pgraster.html. After creating the xml config file proceed to the section Configuring GeoServer in the Image Mosaic JDBC Tutorial