ASoC: dt-bindings: renesas,rz-ssi: Update slave dma channel configuration parameter

The DMAC on RZ/G2L has specific slave channel configuration
parameters for SSI.
This patch updates the dmas description and example node to include
the encoded slave channel configuration.

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Link: https://lore.kernel.org/r/20210813091156.10700-3-biju.das.jz@bp.renesas.com


Signed-off-by: Mark Brown <broonie@kernel.org>