ASoC: topology: Save num_channels value for mixer controls

To provide minimal support for multi-channel kcontrols i.e.: more than
stereo configuration, store the number of channels specified within the
SectionControlMixer. The field is part of the topology standard,
currently skipped by the ASoC core.

Signed-off-by: Cezary Rojewski <cezary.rojewski@intel.com>
Link: https://patch.msgid.link/20250217102115.3539427-3-cezary.rojewski@intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>

include/sound/soc.h

@@ -1254,6 +1254,7 @@ struct soc_mixer_control {
 	int min, max, platform_max;
 	int reg, rreg;
 	unsigned int shift, rshift;
+	u32 num_channels;
 	unsigned int sign_bit;
 	unsigned int invert:1;
 	unsigned int autodisable:1;

sound/soc/soc-topology.c

@@ -669,6 +669,7 @@ static int soc_tplg_control_dmixer_create(struct soc_tplg *tplg, struct snd_kcon
 	sm->min = le32_to_cpu(mc->min);
 	sm->invert = le32_to_cpu(mc->invert);
 	sm->platform_max = le32_to_cpu(mc->platform_max);
+	sm->num_channels = le32_to_cpu(mc->num_channels);
 
 	/* map io handlers */
 	err = soc_tplg_kcontrol_bind_io(&mc->hdr, kc, tplg);