ASoC: dt-bindings: ak4613: switch to yaml base Documentation

This patch switches from .txt base to .yaml base Document.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/87mu4cxlo2.wl-kuninori.morimoto.gx@renesas.com
Link: https://lore.kernel.org/r/87o8pf3923.wl-kuninori.morimoto.gx@renesas.com
Link: https://lore.kernel.org/r/87y2nk2tfd.wl-kuninori.morimoto.gx@renesas.com


Signed-off-by: Mark Brown <broonie@kernel.org>