ASoC: Support registering a DAI dynamically

Define API snd_soc_register_dai() to add a DAI dynamically and
create the DAI widgets. Topology can use this API to register DAIs
when probing a component with topology info. These DAIs's playback
& capture widgets will be freed when the sound card is unregistered
and the DAIs will be freed when cleaning up the component.

And a dobj is embedded into the struct snd_soc_dai_driver. Topology
can use the dobj to find the DAI drivers created by it and free them
when the topology component is removed.

Signed-off-by: Mengdong Lin <mengdong.lin@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
diff --git a/include/sound/soc-dai.h b/include/sound/soc-dai.h
index 212eaaf..964b7de 100644
--- a/include/sound/soc-dai.h
+++ b/include/sound/soc-dai.h
@@ -222,6 +222,7 @@
 	const char *name;
 	unsigned int id;
 	unsigned int base;
+	struct snd_soc_dobj dobj;
 
 	/* DAI driver callbacks */
 	int (*probe)(struct snd_soc_dai *dai);