DT: bindings: net: nfc: Add ST95HF binding doc

This patch includes ST95HF binding doc that guides how to
make node entry of ST95HF in DT file of any platform.
Signed-off-by: NShikha Singh <shikha.singh@st.com>
Signed-off-by: NSamuel Ortiz <sameo@linux.intel.com>

Documentation/devicetree/bindings/net/nfc/st95hf.txt

+* STMicroelectronics : NFC Transceiver ST95HF
+
+ST NFC Transceiver is required to attach with SPI bus.
+ST95HF node should be defined in DT as SPI slave device of SPI
+master with which ST95HF transceiver is physically connected.
+The properties defined below are required to be the part of DT
+to include ST95HF transceiver into the platform.
+
+Required properties:
+===================
+- reg: Address of SPI slave "ST95HF transceiver" on SPI master bus.
+
+- compatible: should be "st,st95hf" for ST95HF NFC transceiver
+
+- spi-max-frequency: Max. operating SPI frequency for ST95HF
+	transceiver.
+
+- enable-gpio: GPIO line to enable ST95HF transceiver.
+
+- interrupt-parent : Standard way to specify the controller to which
+	ST95HF transceiver's interrupt is routed.
+
+- interrupts : Standard way to define ST95HF transceiver's out
+	interrupt.
+
+Optional property:
+=================
+- st95hfvin-supply : This is an optional property. It contains a
+	phandle to ST95HF transceiver's regulator supply node in DT.
+
+Example:
+=======
+spi@9840000 {
+	reg = <0x9840000 0x110>;
+	#address-cells = <1>;
+	#size-cells = <0>;
+	cs-gpios = <&pio0 4>;
+	status = "okay";
+
+	st95hf@0{
+		reg = <0>;
+		compatible = "st,st95hf";
+		status = "okay";
+		spi-max-frequency = <1000000>;
+		enable-gpio = <&pio4 0>;
+		interrupt-parent = <&pio0>;
+		interrupts = <7 IRQ_TYPE_EDGE_FALLING>;
+	};
+
+};