ASoC: rsnd: enable multiple DVC valume settings

DVC controls some digital volume features.
Some of them requests values for "each channels",
but, some of them requests values for "feature".
Current dvc.c is supporting Mute/Volume,
and these have "each channels" settings.
This patch adds rsnd_dvc_cfg_m and care about
multiple settings for each channels.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Mark Brown <broonie@kernel.org>