ALSA: oxygen: Xonar DG(X): move the mixer code into another file

Moving the mixer code away makes things easier. The mixer
will control the driver, so the functions of the
driver need to be non-static.

Signed-off-by: Roman Volkov <v1ron@mail.ru>
Signed-off-by: Clemens Ladisch <clemens@ladisch.de>

sound/pci/oxygen/Makefile

@@ -1,5 +1,5 @@
 snd-oxygen-lib-objs := oxygen_io.o oxygen_lib.o oxygen_mixer.o oxygen_pcm.o
-snd-oxygen-objs := oxygen.o xonar_dg.o
+snd-oxygen-objs := oxygen.o xonar_dg_mixer.o xonar_dg.o
 snd-virtuoso-objs := virtuoso.o xonar_lib.o \
 	xonar_pcm179x.o xonar_cs43xx.o xonar_wm87x6.o xonar_hdmi.o