spi: dw-apb-ssi: Integrate Renesas RZ/N1 SPI controller

Originally, the Renesas RZ/N1 SPI Controller DT bindings were not
integrated in the main DT bindings for the Synopsys DesignWare
Synchronous Serial Interface, but in its own file, as the RZ/N1
controller has additional registers for software CS control and DMA.

As so far DMA is not supported on RZ/N1, and json-schema can handle any
possible differences fine, integrate the RZ/N1 compatible values in the
main DT bindings for the Synopsys DW SSI.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/aef15aa119ed02487ded4691141678bc1040c3b4.1620301936.git.geert+renesas@glider.be


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