ASoC: rsnd: use mod base common method on DMA phase1

Renesas sound needs many devices
(SSI/SSIU/SRC/CTU/MIX/DVC/CMD/AudioDMAC/AudioDMACpp).
SSI/SRC/CTU/MIX/DVC are implemented as module.
SSI parent, SSIU are implemented as part of SSI
CMD is implemented as part of CTU/MIX/DVC
AudioDMAC/AudioDMACpp are implemented as part of SSI/SRC
It is nice sense that these all devices are implemented as mod.

DMA will be implemented as module. Then rsnd_dma will be mod base.
This patch makes rsnd_dma mod base, but still not yet completely
finished. This mod is not yet installed to system at this point.

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