dm: sound: Move common code out of maxim98095

The register-access code is useful for any maxim codec. Move it out into
its own file.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/sound/Makefile b/drivers/sound/Makefile
index 75fa31e..b088455 100644
--- a/drivers/sound/Makefile
+++ b/drivers/sound/Makefile
@@ -15,4 +15,4 @@
 obj-$(CONFIG_I2S)	+= sound-i2s.o
 endif
 obj-$(CONFIG_SOUND_WM8994)	+= wm8994.o
-obj-$(CONFIG_SOUND_MAX98095)	+= max98095.o
+obj-$(CONFIG_SOUND_MAX98095)	+= max98095.o maxim_codec.o