spi: lpspi: add imx8qxp compatible string

Add imx8qxp compatible string
Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/spi/spi-fsl-lpspi.txt

@@ -3,6 +3,7 @@
 Required properties:
 - compatible :
   - "fsl,imx7ulp-spi" for LPSPI compatible with the one integrated on i.MX7ULP soc
+  - "fsl,imx8qxp-spi" for LPSPI compatible with the one integrated on i.MX8QXP soc
 - reg : address and length of the lpspi master registers
 - interrupts : lpspi interrupt
 - clocks : lpspi clock specifier