dt-bindings: i2c: lpi2c: add imx8qm compatible string

Add imx8qm compatible string.
Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/i2c/i2c-imx-lpi2c.txt

@@ -4,6 +4,7 @@ Required properties:
 - compatible :
   - "fsl,imx7ulp-lpi2c" for LPI2C compatible with the one integrated on i.MX7ULP soc
   - "fsl,imx8qxp-lpi2c" for LPI2C compatible with the one integrated on i.MX8QXP soc
+  - "fsl,imx8qm-lpi2c" for LPI2C compatible with the one integrated on i.MX8QM soc
 - reg : address and length of the lpi2c master registers
 - interrupts : lpi2c interrupt
 - clocks : lpi2c clock specifier