nvmem: Add i.MX6 OCOTP device tree binding documentation

Freescale i.MX6 On-Chip OTP Controller (OCOTP) device tree bindings

This binding represents the on-chip eFuse OTP controller found on

i.MX6Q/D, i.MX6DL/S, i.MX6SL, and i.MX6SX SoCs.

Required properties:

- compatible: should be one of

	"fsl,imx6q-ocotp" (i.MX6Q/D/DL/S),

	"fsl,imx6sl-ocotp" (i.MX6SL), or

	"fsl,imx6sx-ocotp" (i.MX6SX), followed by "syscon".

- reg: Should contain the register base and length.

- clocks: Should contain a phandle pointing to the gated peripheral clock.

Example:

	ocotp: ocotp@021bc000 {

		compatible = "fsl,imx6q-ocotp", "syscon";

		reg = <0x021bc000 0x4000>;

		clocks = <&clks IMX6QDL_CLK_IIM>;

	};