ASoC: use helper function and cleanup

Merge series from Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>:

struct snd_soc_dai need to have info for playback/capture,
but it is using "playback/capture_xxx" or "tx/tx_xxx" or array.
This kind of random definition is very difficult to read.

This patch-set add helper functions and each driver use it.
And cleanup the definition.