ASoC: add snd_soc_get_dai_id() function

ALSA SoC needs to know connected DAI ID for detecting.
It is not a big problem if device/driver was only for sound,
but getting DAI ID will be difficult if device includes both
Video/Sound, like HDMI.
To solve this issue, this patch adds new snd_soc_get_dai_id() and
its related .of_xlate_dai_id callback on component driver.
In below case, we can handle Sound port (= port@2) as ID = 0
if .of_xlate_dai_id has its support.

	hdmi {
		port@0 { /* VIDEO */ };
		port@1 { /* VIDEO */ };
		port@2 { /* SOUND */ };
	};

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Mark Brown <broonie@kernel.org>