dt-bindings: nvmem: Add i.MX IIM binding doc

The IIM is part of the i.MX device trees for long already, add a binding
document for it.
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/nvmem/imx-iim.txt

+Freescale i.MX IC Identification Module (IIM) device tree bindings
+
+This binding represents the IC Identification Module (IIM) found on
+i.MX25, i.MX27, i.MX31, i.MX35, i.MX51 and i.MX53 SoCs.
+
+Required properties:
+- compatible: should be one of
+	"fsl,imx25-iim", "fsl,imx27-iim",
+	"fsl,imx31-iim", "fsl,imx35-iim",
+	"fsl,imx51-iim", "fsl,imx53-iim",
+- reg: Should contain the register base and length.
+- interrupts: Should contain the interrupt for the IIM
+- clocks: Should contain a phandle pointing to the gated peripheral clock.
+
+Example:
+
+	iim: iim@63f98000 {
+		compatible = "fsl,imx53-iim", "fsl,imx27-iim";
+		reg = <0x63f98000 0x4000>;
+		interrupts = <69>;
+                clocks = <&clks IMX5_CLK_IIM_GATE>;
+	};