hal: tear down a2dp path for non-offloaded streams when suspended

When A2dp device is already active and A2dpsuspended=true is
received, audio route will be switched to sco mic and BT
firmware will open the RX path as 8KHz, while a2dp playback
can still keep sending data over slimbus, this can cause noise
heard in the BT headset.
To avoid this, tear down the A2dp playback before SCO is enabled.

Change-Id: Ic0b8d1c725340a3a2878d11717631c45c81dc721