ASoC: rsnd: makes volume ramp rate list generic

DVC is supporting Volume Ramp Rate, and MIX has Volume Ramp
but not yet supported. To support MIX Volume Ramp, we want to
share Rate List since DVC/MIX are using almost same list.
This patch move DVC specific Volume Ramp Rate List to core.c.

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>