ASoC: Allow idle_bias_off to be specified in CODEC drivers

If devices can unconditionally support idle_bias_off let them flag it in
their driver structure.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Liam Girdwood <lrg@ti.com>

include/sound/soc.h

@@ -633,6 +633,7 @@ struct snd_soc_codec_driver {
 	/* codec bias level */
 	int (*set_bias_level)(struct snd_soc_codec *,
 			      enum snd_soc_bias_level level);
+	bool idle_bias_off;
 
 	void (*seq_notifier)(struct snd_soc_dapm_context *,
 			     enum snd_soc_dapm_type, int);