NVIDIA Tegra20/Tegra30/Tegra114 I2C controller driver.

Required properties:
- compatible : should be:
	"nvidia,tegra114-i2c"
	"nvidia,tegra30-i2c"
	"nvidia,tegra20-i2c"
	"nvidia,tegra20-i2c-dvc"
  Details of compatible are as follows:
  nvidia,tegra20-i2c-dvc: Tegra20 has specific I2C controller called as DVC I2C
	controller. This only support master mode of I2C communication. Register
	interface/offset and interrupts handling are different than generic I2C
	controller. Driver of DVC I2C controller is only compatible with
	"nvidia,tegra20-i2c-dvc".
  nvidia,tegra20-i2c: Tegra20 has 4 generic I2C controller. This can support
	master and slave mode of I2C communication. The i2c-tegra driver only
	support master mode of I2C communication. Driver of I2C controller is
	only compatible with "nvidia,tegra20-i2c".
  nvidia,tegra30-i2c: Tegra30 has 5 generic I2C controller. This controller is
	very much similar to Tegra20 I2C controller with additional feature:
	Continue Transfer Support. This feature helps to implement M_NO_START
	as per I2C core API transfer flags. Driver of I2C controller is
	compatible with "nvidia,tegra30-i2c" to enable the continue transfer
	support. This is also compatible with "nvidia,tegra20-i2c" without
	continue transfer support.
  nvidia,tegra114-i2c: Tegra114 has 5 generic I2C controller. This controller is
	very much similar to Tegra30 I2C controller with some hardware
	modification:
	 - Tegra30/Tegra20 I2C controller has 2 clock source called div-clk and
	   fast-clk. Tegra114 has only one clock source called as div-clk and
	   hence clock mechanism is changed in I2C controller.
	 - Tegra30/Tegra20 I2C controller has enabled per packet transfer by
	   default and there is no way to disable it. Tegra114 has this
	   interrupt disable by default and SW need to enable explicitly.
	Due to above changes, Tegra114 I2C driver makes incompatible with
	previous hardware driver. Hence, tegra114 I2C controller is compatible
	with "nvidia,tegra114-i2c".
- reg: Should contain I2C controller registers physical address and length.
- interrupts: Should contain I2C controller interrupts.
- address-cells: Address cells for I2C device address.
- size-cells: Size of the I2C device address.
- clocks: Clock ID as per
		Documentation/devicetree/bindings/clock/tegra<chip-id>.txt
	for I2C controller.
- clock-names: Name of the clock:
	Tegra20/Tegra30 I2C controller: "div-clk and "fast-clk".
	Tegra114 I2C controller: "div-clk".

Example:

	i2c@7000c000 {
		compatible = "nvidia,tegra20-i2c";
		reg = <0x7000c000 0x100>;
		interrupts = <0 38 0x04>;
		#address-cells = <1>;
		#size-cells = <0>;
		clocks = <&tegra_car 12>, <&tegra_car 124>;
		clock-names = "div-clk", "fast-clk";
		status = "disabled";
	};
