audio: add linein to BT headset loopback support

- Add AUDIO_DEVICE_OUT_BLUETOOTH_A2DP as the sink
  device to support linein to BT headset loopback.
- set device_connect parameter in transcode loopback
  test app to load A2DP source IPC library.

Change-Id: Ib52fdf9aa966f50834ffa34884f5fa76053df15e
diff --git a/hal/audio_hw.c b/hal/audio_hw.c
index dace3ac..798a697 100644
--- a/hal/audio_hw.c
+++ b/hal/audio_hw.c
@@ -2345,6 +2345,8 @@
              }
          } else if ((usecase->stream.out != NULL) &&
               !(usecase->stream.out->flags & AUDIO_OUTPUT_FLAG_COMPRESS_OFFLOAD) &&
+              (usecase->type != TRANSCODE_LOOPBACK_TX) &&
+              (usecase->type != TRANSCODE_LOOPBACK_RX) &&
               usecase->stream.out->started) {
               if (is_bt_soc_on(adev) == false) {
                   ALOGD("BT SCO/A2dp disconnected while in connection");