dt-bindings: spi: nxp-fspi: add imx8ulp support

The flexspi on imx8ulp only has 16 number of LUTs, it is different
with flexspi on other imx SoC which has 32 number of LUTs.

Fixes: ef89fd5 ("arm64: dts: imx8ulp: add flexspi node")
Cc: stable@kernel.org
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Haibo Chen <haibo.chen@nxp.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Link: https://patch.msgid.link/20240905094338.1986871-2-haibo.chen@nxp.com
Signed-off-by: Mark Brown <broonie@kernel.org>

Author: BoughChen

Documentation/devicetree/bindings/spi/spi-nxp-fspi.yaml

@@ -21,6 +21,7 @@ properties:
           - nxp,imx8mm-fspi
           - nxp,imx8mp-fspi
           - nxp,imx8qxp-fspi
+          - nxp,imx8ulp-fspi
           - nxp,lx2160a-fspi
       - items:
           - enum: