ASoC: add snd_soc_of_get_dai_name() default of_xlate

Current snd_soc_of_get_dai_name() needs .of_xlate_dai_name()
callback on each component drivers.
But required behavior on almost all these drivers is
just returns its indexed driver's name.

This patch adds this feature as default behavior.
.of_xlate_dai_name() can overwrite it.

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