ASoC: rsnd: tidyup ADG

Merge series from Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>:

Renesas Sound has ADG for clock control. Basically it needs
accurately divisible external input clock. But sometimes
sometimes it doesn't have to be accurate for some reason.

We can use ADG clk_i for such case. It came from CPG as
very high rate clock, but is not accurately divisible for
48kHz/44.1kHz rate, but enough for approximate rate.

This patch set support such use case.