NFC: trf7970a: Add DTS Documentation

* Texas Instruments TRF7970A RFID/NFC/15693 Transceiver

Required properties:

- compatible: Should be "ti,trf7970a".

- spi-max-frequency: Maximum SPI frequency (<= 2000000).

- interrupt-parent: phandle of parent interrupt handler.

- interrupts: A single interrupt specifier.

- ti,enable-gpios: Two GPIO entries used for 'EN' and 'EN2' pins on the

  TRF7970A.

- vin-supply: Regulator for supply voltage to VIN pin

Optional SoC Specific Properties:

- pinctrl-names: Contains only one value - "default".

- pintctrl-0: Specifies the pin control groups used for this controller.

Example (for ARM-based BeagleBone with TRF7970A on SPI1):

&spi1 {

	status = "okay";

	nfc@0 {

		compatible = "ti,trf7970a";

		reg = <0>;

		pinctrl-names = "default";

		pinctrl-0 = <&trf7970a_default>;

		spi-max-frequency = <2000000>;

		interrupt-parent = <&gpio2>;

		interrupts = <14 0>;

		ti,enable-gpios = <&gpio2 2 GPIO_ACTIVE_LOW>,

				  <&gpio2 5 GPIO_ACTIVE_LOW>;

		vin-supply = <&ldo3_reg>;

		status = "okay";

	};

};

F:	include/uapi/linux/nfc.h

F:	drivers/nfc/

F:	include/linux/platform_data/pn544.h

F:	Documentation/devicetree/bindings/net/nfc/

NFS, SUNRPC, AND LOCKD CLIENTS

M:	Trond Myklebust <trond.myklebust@primarydata.com>