arm64: dts: renesas: r8a7796: Enable DMA for SCIF2

SCIF2 on R-Car M3-W can be used with both DMAC1 and DMAC2.

Fixes: dbcae5ea ("arm64: dts: r8a7796: Enable SCIF DMA")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>