ASoC: rsnd: add rsnd_kctrl_xxx() macro

Current CTU/MIX/DVC are directly using rsnd_kctrl_cfg_m/s to control
val etc, but it is difficult to read/understand.
And there was no uniformity in access method.
This patch adds new rsnd_kctrl_xxx() and implements uniformed access
method.

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