ASoC: rsnd: add struct rsnd_dvc_cfg and control DVC settings

DVC can control Digital Volume / Mute / Volume Ramp etc,
and these uses different max value.
Current driver is using fixed max value for each settings.
This patch adds new struct rsnd_dvc_cfg, and control these.

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