ASoC: add output/input widgets in ad1938 to make dac/adc dynamic PM work

According to the function dapm_dac_check_power() in
sound/soc/soc-dapm.c, dac power can't be on/off stand-alone without any
output widget as sink. And according to dapm_adc_check_power(), adc
power can't be on/off stand-alone without any input widget as source. So
we can't only define some stand-alone SND_SOC_DAPM_DAC/SND_SOC_DAPM_ADC
to hope their power can be managed dynamically.
Signed-off-by: Barry Song <21cnbao@gmail.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

sound/soc/codecs/ad1938.c

@@ -99,11 +99,23 @@ static const struct snd_soc_dapm_widget ad1938_dapm_widgets[] = {
 	SND_SOC_DAPM_DAC("DAC", "Playback", AD1938_DAC_CTRL0, 0, 1),
 	SND_SOC_DAPM_ADC("ADC", "Capture", SND_SOC_NOPM, 0, 0),
 	SND_SOC_DAPM_SUPPLY("ADC_PWR", AD1938_ADC_CTRL0, 0, 1, NULL, 0),
+	SND_SOC_DAPM_OUTPUT("DAC1OUT"),
+	SND_SOC_DAPM_OUTPUT("DAC2OUT"),
+	SND_SOC_DAPM_OUTPUT("DAC3OUT"),
+	SND_SOC_DAPM_OUTPUT("DAC4OUT"),
+	SND_SOC_DAPM_INPUT("ADC1IN"),
+	SND_SOC_DAPM_INPUT("ADC2IN"),
 };
 
 static const struct snd_soc_dapm_route audio_paths[] = {
 	{ "DAC", NULL, "ADC_PWR" },
 	{ "ADC", NULL, "ADC_PWR" },
+	{ "DAC1OUT", "DAC1 Switch", "DAC" },
+	{ "DAC2OUT", "DAC2 Switch", "DAC" },
+	{ "DAC3OUT", "DAC3 Switch", "DAC" },
+	{ "DAC4OUT", "DAC4 Switch", "DAC" },
+	{ "ADC", "ADC1 Switch", "ADC1IN" },
+	{ "ADC", "ADC2 Switch", "ADC2IN" },
 };
 
 /*