ALSA/ASoC: use snd_pcm_direction_name()

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

Many drivers are selecting strings "playback" / "capture" by own
handling, but we have snd_pcm_direction_name() function for it.
This patch use it.

One note is that snd_pcm_direction_name() will select
"Playback" and "Capture", instead of "playback" / "capture".
Almost all drivers are using it as dev_dbg() or dev_err()
so no problem. But some other drivers are using it as other
purpose. It might be issue (?). For example ASoC debugfs dir name
will be changed by this patch.