arm64: dts: r8a7795: Complete SYS-DMAC nodes

Complete the dma-controller nodes for SYS-DMAC 0 to 2.

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