ASoC: sun4i-codec: Add Mic Playback Volume

Add a control "Mic Playback Volume" that allows the user to control the
MIC gain stage (common for Mic1 and Mic2) leading to the output mixer.
Signed-off-by: NDanny Milosavljevic <dannym@scratchpost.org>
Reviewed-by: NChen-Yu Tsai <wens@csie.org>
Signed-off-by: NMark Brown <broonie@kernel.org>

sound/soc/sunxi/sun4i-codec.c

@@ -681,6 +681,9 @@ static const struct snd_kcontrol_new sun4i_codec_controls[] = {
 	SOC_SINGLE_TLV("Power Amplifier Volume", SUN4I_CODEC_DAC_ACTL,
 		       SUN4I_CODEC_DAC_ACTL_PA_VOL, 0x3F, 0,
 		       sun4i_codec_pa_volume_scale),
+	SOC_SINGLE_TLV("Mic Playback Volume", SUN4I_CODEC_DAC_ACTL,
+		       SUN4I_CODEC_DAC_ACTL_MICG, 7, 0,
+		       sun4i_codec_micin_loopback_gain_scale),
 };
 
 static const struct snd_kcontrol_new sun4i_codec_left_mixer_controls[] = {