arm64: dts: renesas: r8a7796: Tie Audio-DMAC to IPMMU-MP

Hook up r8a7796 Audio-DMAC nodes to the IPMMU-MP.

Based on work for the r8a7795 by Magnus Damm.

Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>