dt-bindings: spi: imx: Add an entry for the i.MX8QM compatible

Add an entry for the "fsl,imx8mq-ecspi" compatible to describe
the ECSPI version present on i.MX8M.
Signed-off-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

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

@@ -10,6 +10,7 @@ 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
 - 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.