ASoC: add soc-link.c

Current ALSA SoC has many dai_link->xxx() functions.
But, it is implemented randomly at random place.

This patch creats new soc-link.c and collect dai_link related
operation into it.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Reviewed-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/871rn84ys5.wl-kuninori.morimoto.gx@renesas.com
Signed-off-by: Mark Brown <broonie@kernel.org>

include/sound/soc-link.h

@@ -0,0 +1,13 @@
+/* SPDX-License-Identifier: GPL-2.0
+ *
+ * soc-link.h
+ *
+ * Copyright (C) 2019 Renesas Electronics Corp.
+ * Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
+ */
+#ifndef __SOC_LINK_H
+#define __SOC_LINK_H
+
+int snd_soc_link_init(struct snd_soc_pcm_runtime *rtd);
+
+#endif /* __SOC_LINK_H */