dt-bindings: spi: imx: Add i.MX8MM/i.MX8MN/i.MX8MP compatible

Add compatible for imx8mm/imx8mn/imx8mp.
Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/1581425307-18567-1-git-send-email-Anson.Huang@nxp.comSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/spi/fsl-imx-cspi.txt

@@ -10,7 +10,10 @@ Required properties:
   - "fsl,imx35-cspi" for SPI compatible with the one integrated on i.MX35
   - "fsl,imx51-ecspi" for SPI compatible with the one integrated on i.MX51
   - "fsl,imx53-ecspi" for SPI compatible with the one integrated on i.MX53 and later Soc
-  - "fsl,imx8mq-ecspi" for SPI compatible with the one integrated on i.MX8M
+  - "fsl,imx8mq-ecspi" for SPI compatible with the one integrated on i.MX8MQ
+  - "fsl,imx8mm-ecspi" for SPI compatible with the one integrated on i.MX8MM
+  - "fsl,imx8mn-ecspi" for SPI compatible with the one integrated on i.MX8MN
+  - "fsl,imx8mp-ecspi" for SPI compatible with the one integrated on i.MX8MP
 - reg : Offset and length of the register set for the device
 - interrupts : Should contain CSPI/eCSPI interrupt
 - clocks : Clock specifiers for both ipg and per clocks.