ASoC: rsnd: add sample code of rcar_sound,src irq

cfcefe01
(ASoC: rsnd: add recovery support for under/over flow error on SRC)
added SRC recovery support which needs IRQ.
This patch adds SRC irq sample code on DT bingdings text

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