ASoC: rsnd: DVC kctrl sets once

Same DVC might be used few times if system/platform is using MIX.
For example below case.

	DAI0 playback = <&src0 &ctu02 &mix0 &dvc0 &ssi0>;
	DAI1 playback = <&src2 &ctu03 &mix0 &dvc0 &ssi0>;

This case, ALSA will have DVC,0 and DVC,1 kcontrol interfaces,
but these are same DVC. This is confusing.
This patch adds new flags and avoid such case.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Tested-by: Hiroyuki Yokoyama <hiroyuki.yokoyama.vx@renesas.com>
Signed-off-by: Mark Brown <broonie@kernel.org>