ASoC: codecs/jz4760: add digital gain controls

Both the DAC and ADC have digital gain controls available
for their mixers, which go from -31 to 0db by step of 1db.
Signed-off-by: Christophe Branchereau <cbranchereau@gmail.com>
Link: https://lore.kernel.org/r/20230122210703.2552384-1-cbranchereau@gmail.comSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/jz4760.c

@@ -287,6 +287,7 @@ static const DECLARE_TLV_DB_MINMAX_MUTE(dac_tlv, -3100, 100);
 static const DECLARE_TLV_DB_SCALE(adc_tlv, 0, 100, 0);
 static const DECLARE_TLV_DB_MINMAX(out_tlv, -2500, 100);
 static const DECLARE_TLV_DB_SCALE(linein_tlv, -2500, 100, 0);
+static const DECLARE_TLV_DB_MINMAX(mixer_tlv, -3100, 0);
 
 /* Unconditional controls. */
 static const struct snd_kcontrol_new jz4760_codec_snd_controls[] = {
@@ -299,6 +300,14 @@ static const struct snd_kcontrol_new jz4760_codec_snd_controls[] = {
 			 JZ4760_CODEC_REG_GCR4, JZ4760_CODEC_REG_GCR3,
 			 REG_GCR_GAIN_OFFSET, REG_GCR_GAIN_MAX, 1, linein_tlv),
 
+	SOC_SINGLE_TLV("Mixer Capture Volume",
+		       JZ4760_CODEC_REG_MIX1,
+		       REG_GCR_GAIN_OFFSET, REG_GCR_GAIN_MAX, 1, mixer_tlv),
+
+	SOC_SINGLE_TLV("Mixer Playback Volume",
+		       JZ4760_CODEC_REG_MIX2,
+		       REG_GCR_GAIN_OFFSET, REG_GCR_GAIN_MAX, 1, mixer_tlv),
+
 	SOC_SINGLE("High-Pass Filter Capture Switch",
 		   JZ4760_CODEC_REG_CR4,
 		   REG_CR4_ADC_HPF_OFFSET, 1, 0),