ASoC: ac97: Support multi-platform AC'97

Currently we can only have a single platform built in with AC'97 support
due to the use of a global variable to provide the bus operations. Fix
this by making that variable a pointer and having the bus drivers set the
operations prior to registering.

This is not a particularly good or nice approach but it avoids blocking
multiplatform and a real fix involves fixing the fairly deep problems
with AC'97 support - we should be converting it to a real bus.

Acked-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Mark Brown <broonie@linaro.org>

sound/soc/soc-core.c

@@ -2079,6 +2079,22 @@ int snd_soc_new_ac97_codec(struct snd_soc_codec *codec,
 }
 EXPORT_SYMBOL_GPL(snd_soc_new_ac97_codec);
 
+struct snd_ac97_bus_ops *soc_ac97_ops;
+
+int snd_soc_set_ac97_ops(struct snd_ac97_bus_ops *ops)
+{
+	if (ops == soc_ac97_ops)
+		return 0;
+
+	if (soc_ac97_ops && ops)
+		return -EBUSY;
+
+	soc_ac97_ops = ops;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(snd_soc_set_ac97_ops);
+
 /**
  * snd_soc_free_ac97_codec - free AC97 codec device
  * @codec: audio codec