ASoC: soc-dapm: move snd_soc_dapm_get_bias_level() to soc-dpcm

ASoC: soc-dapm: move snd_soc_dapm_get_bias_level() to soc-dpcm

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.

Because dapm will not be used on user driver in the future, Let's move
snd_soc_dapm_get_bias_level() to soc-dpcm.c

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Link: https://patch.msgid.link/874iul83ju.wl-kuninori.morimoto.gx@renesas.com
Signed-off-by: Mark Brown <broonie@kernel.org>