[ALSA] Move vmaster code to sound core

Move the codes for virtual master controls to sound core part so that
not only hda-intel drivers can use it.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/sound/core/Kconfig b/sound/core/Kconfig
index 829ca38..a8d71c6 100644
--- a/sound/core/Kconfig
+++ b/sound/core/Kconfig
@@ -181,3 +181,7 @@
 	  It is usually not required, but if you have trouble with
 	  sound clicking when system is loaded, it may help to determine
 	  the process or driver which causes the scheduling gaps.
+
+config SND_VMASTER
+	bool
+	depends on SND