Enable DMA transfer to/from SSIU in gose/r8a7791 device tree.

     DMA
[MEM] -> [SSIU] -> [SSI]

     DMA
[MEM] <- [SSIU] <- [SSI]

Based on similar work for the r8a7791/koelsch 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>