ASoC: unpack snd_soc_component_xxx_bias_level()

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

Because struct snd_soc_dapm_context is soc-dapm framework specific, user
driver don't need to access its member directly, we would like to hide
them. struct snd_soc_dapm_context will be removed from header in the
future.

This is prepare patch for it.