ASoC: SOF: Intel: hda: Add a virtual CPU DAI

Add a virtual CPU DAI for loopback capture for echo reference
implementation. We can't use the snd-soc-dummy-dai because it is already
used for the bluetooth DAI link.

Signed-off-by: Ranjani Sridharan <[e-mail]>
Reviewed-by: Bard Liao <[e-mail]>
Reviewed-by: Liam Girdwood <[e-mail]>
Reviewed-by: Mateusz Redzynia <[e-mail]>
Signed-off-by: Peter Ujfalusi <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Mark Brown <[e-mail]>

sound/soc/sof/intel/hda-dai.c

···
 		.channels_max = 4,
 	},
 },
+{
+	/* Virtual CPU DAI for Echo reference */
+	.name = "Loopback Virtual Pin",
+	.capture = {
+		.channels_min = 1,
+		.channels_max = 2,
+	},
+},
 #if IS_ENABLED(CONFIG_SND_SOC_SOF_HDA_AUDIO_CODEC)
 {
 	.name = "iDisp1 Pin",

sound/soc/sof/intel/hda.h

···
 	(HDA_DSP_BDL_SIZE / sizeof(struct sof_intel_dsp_bdl))
 
 /* Number of DAIs */
-#define SOF_SKL_NUM_DAIS_NOCODEC	8
+#define SOF_SKL_NUM_DAIS_NOCODEC	9
 
 #if IS_ENABLED(CONFIG_SND_SOC_SOF_HDA_AUDIO_CODEC)
-#define SOF_SKL_NUM_DAIS		15
+#define SOF_SKL_NUM_DAIS		16
 #else
 #define SOF_SKL_NUM_DAIS		SOF_SKL_NUM_DAIS_NOCODEC
 #endif