asoc: add support for afe_loopback_tx BE dai

Add dai driver and routing driver changes for
afe loopback BE. This BE is used to capture
EC reference data.

Change-Id: Ia57f335bde5f8a47de0030fbf1cdb784c8821e17
Signed-off-by: Surendar Karka <skarka@codeaurora.org>

dsp/q6afe.c

@@ -4584,6 +4584,8 @@ int afe_get_port_index(u16 port_id)
 		return IDX_AFE_PORT_ID_RX_CODEC_DMA_RX_6;
 	case AFE_PORT_ID_RX_CODEC_DMA_RX_7:
 		return IDX_AFE_PORT_ID_RX_CODEC_DMA_RX_7;
+	case AFE_LOOPBACK_TX:
+		return IDX_AFE_LOOPBACK_TX;
 	default:
 		pr_err("%s: port 0x%x\n", __func__, port_id);
 		return -EINVAL;