ASoC: dt-bindings: renesas,rz-ssi: Document RZ/G2UL SoC

Document RZ/G2U2L SSI bindings. RZ/G2UL SSI is identical to one found
on the RZ/G2L SoC. No driver changes are required as generic compatible
string "renesas,rz-ssi" will be used as a fallback.

While at it add a '.' at the end of dmas description for the first cell.

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20220607124231.3248-1-biju.das.jz@bp.renesas.com
Signed-off-by: Mark Brown <broonie@kernel.org>