ARM: shmobile: r8a7791 dtsi: Enable DMA for MSIOF

Add register sets used for access by the DMA engine, and DMA properties to
the MSIOF nodes.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>