dt-bindings: i2c: imx-lpi2c: add devicetree bindings

Add a binding document for lpi2c driver.
Signed-off-by: NGao Pan <pandy.gao@nxp.com>
Signed-off-by: NWolfram Sang <wsa@the-dreams.de>

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

+* Freescale Low Power Inter IC (LPI2C) for i.MX
+
+Required properties:
+- compatible :
+  - "fsl,imx7ulp-lpi2c" for LPI2C compatible with the one integrated on i.MX7ULP soc
+  - "fsl,imx8dv-lpi2c" for LPI2C compatible with the one integrated on i.MX8DV soc
+- reg : address and length of the lpi2c master registers
+- interrupt-parent : core interrupt controller
+- interrupts : lpi2c interrupt
+- clocks : lpi2c clock specifier
+
+Examples:
+
+lpi2c7: lpi2c7@40A50000 {
+	compatible = "fsl,imx8dv-lpi2c";
+	reg = <0x40A50000 0x10000>;
+	interrupt-parent = <&intc>;
+	interrupts = <GIC_SPI 37 IRQ_TYPE_LEVEL_HIGH>;
+	clocks = <&clks IMX7ULP_CLK_LPI2C7>;
+};