ASoC: rsnd: add rsnd_scu_enable_ssi_irq()

Current R-Car sound driver is assuming that
SCU mod is used even though it is not needed.
Because scu.c is controlling SSIU too.
(it is Gen1 compatibility)
But, SCU mod will be really not used if new platform dai
feature was used.
Thus, SSIU irq setting is called from SSI
directory by this patch.

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