ASoC: rsnd: explain extended Audio DMAC peri peri address

ASoC: rsnd: explain extended Audio DMAC peri peri address

If SoC has extended Audio DMAC peri peri address,
DT needs to select it.
Otherwise, it can select normal Audio DMAC peri peri address.
Extended Audio DMAC peri peri address can use BUSIF4-7,
normal address can't.

Reported-by: Jiada Wang <jiada_wang@mentor.com>
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Mark Brown <broonie@kernel.org>