ASoC: rsnd: move snd_kcontrol_new fucntions to core.c

Current DVC is using snd_kcontrol_new functions, but, SRC will need
same method. Move common functions to core.c

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