ASoC: rsnd: add CTU basic support

This patch adds Renesas R-Car sound CTU (= Channel Transfer Unit)
very basic support, but not yet enough feature at this point.
Because CTU support needs more complex channel function for
each modules.
To avoid complex patch reviewing, this patch picked up very basic
part only.

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