Emergency Function HAL (continued)

- Add Emergency Number source for Emergency number, which is critical for
management and display priority.
- Remove solicited request for getting emergency number list.
- Rephrasing the documentations.

Test: Treehugger (will add VTS later)
Bug: 112657134
Change-Id: Idbfebf8d246de06fd91e8de89088f5cc2c70227b