arm64: renesas: salvator-x: Sound SSI DMA support

DMA transfer to/from SSI

     DMA
[MEM] -> [SSI]

     DMA
[MEM] <- [SSI]

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>