Add ability to disable video conferencing.

- Added check for carrier config in TelecomAccountRegistry.
- In TelephonyConnectionService, modified th existing
"setConferenceSupported" check to also check if this is a video call and
if video conferencing is supported.

Bug: 27658118
Change-Id: I222b4d1fb4a1f771394fec01a8300f8bdaffd2db
2 files changed