ASoC: capsuling struct snd_soc_dapm_context

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

Now, all DAPM users are using function to handling it.
We can capsuling it. This patchset moves struct snd_soc_dapm_context into
soc-dapm.c, and remove un-used functions.

Link: https://lore.kernel.org/r/87zf7jrx52.wl-kuninori.morimoto.gx@renesas.com