ASoC: rsnd: move rsnd_src_ssi_irq_enable/disable() to ssi.c

Part of SSI IRQ enable/disable was controlled by SRU (on Gen1)
or CMD (on Gen2). Because of this reason SSI IRQ function was
implemented under src.c. but it is not understandable.
Let's move it to ssi.c

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