hal: Fix audio mute issue on MT call over a2dp

- Random audio mute issues are seen on BT SCO
  device during MT voice call
- As a part of MT call ringtone playback on a2dp,
  a2dp start request is failing from BT IPC library
  as BT IPC librbary does not support a2dp playback when
  phone state is MODE_IN_RINGTONE/MODE_IN_NORMAL.
  When a2dp playback start fails on low latency,pcm_prepare()
  is called continouly till audio routes to a2dp.
  This impacts voice call routing to sco as primary output/
  low latency session is in improper state.
- Do not route audio to a2dp device if phone state is
  MODE_IN_RINGTONE/MODE_IN_CALL.

Change-Id: Icf1f10c00365b0b401464ebcbe6135fe93a0dd0e