ARM: dts: r8a7793: enable Audio DMAC peri peri via sound driver

Audio DMAC peri peri is no longer DMAEngine. it is supported by
sound driver. this patch enable it.

Base on work for the r8a7791 by Kuninori Morimoto.

Cc: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>