spi: spi-rockchip: Add rk3568-spi compatible

This adds a compatible string for the SPI controller found on
the RK3566 and RK3568 SoCs.
Signed-off-by: Nicolas Frattaroli <frattaroli.nicolas@gmail.com>
Link: https://lore.kernel.org/r/20211126154344.724316-2-frattaroli.nicolas@gmail.comSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/spi/spi-rockchip.yaml

@@ -33,6 +33,7 @@ properties:
               - rockchip,rk3328-spi
               - rockchip,rk3368-spi
               - rockchip,rk3399-spi
+              - rockchip,rk3568-spi
               - rockchip,rv1126-spi
           - const: rockchip,rk3066-spi