* HID over I2C Device-Tree bindings

HID over I2C provides support for various Human Interface Devices over the
I2C bus. These devices can be for example touchpads, keyboards, touch screens
or sensors.

The specification has been written by Microsoft and is currently available here:
http://msdn.microsoft.com/en-us/library/windows/hardware/hh852380.aspx

If this binding is used, the kernel module i2c-hid will handle the communication
with the device and the generic hid core layer will handle the protocol.

Required properties:
- compatible: must be "hid-over-i2c"
- reg: i2c slave address
- hid-descr-addr: HID descriptor address
- interrupt-parent: the phandle for the interrupt controller
- interrupts: interrupt line

Additional optional properties:

Some devices may support additional optional properties to help with, e.g.,
power sequencing. The following properties can be supported by one or more
device-specific compatible properties, which should be used in addition to the
"hid-over-i2c" string.

- compatible:
  * "wacom,w9013" (Wacom W9013 digitizer). Supports:
    - vdd-supply
    - post-power-on-delay-ms

- vdd-supply: phandle of the regulator that provides the supply voltage.
- post-power-on-delay-ms: time required by the device after enabling its regulators
  or powering it on, before it is ready for communication.

Example:

	i2c-hid-dev@2c {
		compatible = "hid-over-i2c";
		reg = <0x2c>;
		hid-descr-addr = <0x0020>;
		interrupt-parent = <&gpx3>;
		interrupts = <3 2>;
	};
