dt-bindings: nfc: Add Documentation for I2C NFC devicetree node

Qualcomm Technologies, Inc SNxxx NFC NCI device

Near Field Communication (NFC) device is based on NFC Controller Interface (NCI)

Required properties:

- compatible: "qcom,sn-nci"

- reg: NCI I2C slave address.

- qcom,sn-ven: specific gpio for hardware reset.

- qcom,sn-irq: specific gpio for read interrupt.

- qcom,sn-firm: gpio for firmware download

- qcom,sn-clkreq: gpio for clock

- interrupt-parent: Should be phandle for the interrupt controller

                    that services interrupts for this device.

- interrupts: Nfc read interrupt,gpio-clk-req interrupt

Recommended properties:

- interrupt-names: names of interrupts, should include "nfc_irq", used for reference

Optional properties:

- pinctrl-names, pinctrl-0, pincntrl-1: references to our pincntrl settings

- clocks, clock-names: must contain the SNxxx's core clock.

- qcom,clk-src: NFC clock for antenna

Example:

	sn-nci@2b {

		compatible = "qcom,sn-nci";

		reg = <0x2b>;

		qcom,sn-irq = <&tlmm 87 0x00>;

		qcom,sn-ven = <&tlmm 62 0x00>;

		qcom,sn-firm = <&tlmm 86 0x00>;

		qcom,sn-clkreq = <&tlmm 63 0x00>;

		qcom,clk-src = "BBCLK2";

		interrupt-parent = <&tlmm>;

		interrupts = <29 0>;

		interrupt-names = "nfc_irq";

		pinctrl-names = "default","sleep";

		pinctrl-0 = <&nfc_enable_active &nfc_fwdl_active

				&nfc_clk_req_active &nfc_int_active>;

		pinctrl-1 = <&nfc_enable_suspend &nfc_fwdl_suspend

				&nfc_clk_req_suspend &nfc_int_suspend>;

		clocks = <&clock_rpm clk_bb_clk2_pin>;

		clock-names = "ref_clk";

		status = "ok";

	};