[ALSA] Add helper functions for frequently used callbacks

Added helper functions for frequenty used callbacks:
  snd_ctl_boolean_mono_info() and snd_ctl_boolean_stereo_info()

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>
diff --git a/include/sound/control.h b/include/sound/control.h
index 72e759f..b26d463 100644
--- a/include/sound/control.h
+++ b/include/sound/control.h
@@ -161,4 +161,12 @@
 	return dst_id;
 }
 
+/*
+ * Frequently used control callbacks
+ */
+int snd_ctl_boolean_mono_info(struct snd_kcontrol *kcontrol,
+			      struct snd_ctl_elem_info *uinfo);
+int snd_ctl_boolean_stereo_info(struct snd_kcontrol *kcontrol,
+				struct snd_ctl_elem_info *uinfo);
+
 #endif	/* __SOUND_CONTROL_H */