ASoC: dt-bindings: renesas,rsnd.yaml: drop "dmas/dma-names" from "rcar_sound,ssi"

SSI is supporting both "PIO mode" and "DMA mode", thus "dmas/dma-names"
are not mandatory property. Drop these from rcar_sound,ssi's required:.
This is prepare for Gen4 support. See more details on Link

Link: https://lore.kernel.org/all/87zg9vk0ex.wl-kuninori.morimoto.gx@renesas.com/#r
Link: https://lore.kernel.org/all/87r0v2uvm7.wl-kuninori.morimoto.gx@renesas.com/#r
Link: https://lore.kernel.org/all/87r0v1t02h.wl-kuninori.morimoto.gx@renesas.com/#r
Link: https://lore.kernel.org/all/87y1p7bpma.wl-kuninori.morimoto.gx@renesas.com/#r


Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/87r0uu8g8x.wl-kuninori.morimoto.gx@renesas.com


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