ASoC: rsnd: extracts Gen1/Gen2 common parts

Renesas sound IP Gen1/Gen2 are similar, but different.
This patch extracts Gen1/Gen2 common and dependency parts,
and create Gen1/Gen2 ops to control it.

According to this structure, SSIU setup which
has been implemented on ssi.c can be moved to scu.c
(SRU/SSIU/SCU should be implemented on scu.c)

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