TIF: Rename R.attr.contentRatingSystemXml and fix documentation

- Rename contentRatingSystemXml to tvContentRatingDescription.
- Change docs to indicate this is a reference to an XML document that
  describes TV content rating, not a component name.
- Replace the DTD with an XML example.

Bug: 16960702
Change-Id: Iea985e9847ee5af0f745e896c498792234308b12
5 files changed