TIF: Add more comments for TvInputInfo/TvTrackInfo

- Documented what TvInputInfo.getTunerCount returns if the input is not
  of TYPE_TUNER.
- Documented what all getters/setters in TvTrackInfo throw if not called
  on proper types.

Bug: 27531254
Change-Id: I32d83ce888507ec29cda8dce74871a3d55783766