ASoC: Factor out shared code from WM8993

The WM8993 analogue control is shared with other devices in the same
product line.  Since this is a very substantial proportion of the
driver move the definitions of these controls into a new wm_hubs module
which allows them to be shared between the two.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
diff --git a/sound/soc/codecs/Kconfig b/sound/soc/codecs/Kconfig
index dd9b295..910b916 100644
--- a/sound/soc/codecs/Kconfig
+++ b/sound/soc/codecs/Kconfig
@@ -64,6 +64,10 @@
 
           If unsure select "N".
 
+config SND_SOC_WM_HUBS
+	tristate
+	default y if SND_SOC_WM8993=y
+	default m if SND_SOC_WM8993=m
 
 config SND_SOC_AC97_CODEC
 	tristate