Switch to speakerphone when upgrading to video

When an audio-only call gets upgraded to a video call, switch to
speakerphone if the call would have been started in speakerphone had it
been a video call from the beginning (i.e. if there's no headset or
bluetooth connected and config options support it)

Change-Id: I4b8eb1c0f21753a8878f72d9279335a946c9f5a9
Fixes: 29563103