NVIDIA Tegra124 DFLL FCPU clocksource

This binding uses the common clock binding:
Documentation/devicetree/bindings/clock/clock-bindings.txt

The DFLL IP block on Tegra is a root clocksource designed for clocking
the fast CPU cluster. It consists of a free-running voltage controlled
oscillator connected to the CPU voltage rail (VDD_CPU), and a closed loop
control module that will automatically adjust the VDD_CPU voltage by
communicating with an off-chip PMIC either via an I2C bus or via PWM signals.
Currently only the I2C mode is supported by these bindings.

Required properties:
- compatible : should be "nvidia,tegra124-dfll"
- reg : Defines the following set of registers, in the order listed:
        - registers for the DFLL control logic.
        - registers for the I2C output logic.
        - registers for the integrated I2C master controller.
        - look-up table RAM for voltage register values.
- interrupts: Should contain the DFLL block interrupt.
- clocks: Must contain an entry for each entry in clock-names.
  See clock-bindings.txt for details.
- clock-names: Must include the following entries:
  - soc: Clock source for the DFLL control logic.
  - ref: The closed loop reference clock
  - i2c: Clock source for the integrated I2C master.
- resets: Must contain an entry for each entry in reset-names.
  See ../reset/reset.txt for details.
- reset-names: Must include the following entries:
  - dvco: Reset control for the DFLL DVCO.
- #clock-cells: Must be 0.
- clock-output-names: Name of the clock output.
- vdd-cpu-supply: Regulator for the CPU voltage rail that the DFLL
  hardware will start controlling. The regulator will be queried for
  the I2C register, control values and supported voltages.

Required properties for the control loop parameters:
- nvidia,sample-rate: Sample rate of the DFLL control loop.
- nvidia,droop-ctrl: See the register CL_DVFS_DROOP_CTRL in the TRM.
- nvidia,force-mode: See the field DFLL_PARAMS_FORCE_MODE in the TRM.
- nvidia,cf: Numeric value, see the field DFLL_PARAMS_CF_PARAM in the TRM.
- nvidia,ci: Numeric value, see the field DFLL_PARAMS_CI_PARAM in the TRM.
- nvidia,cg: Numeric value, see the field DFLL_PARAMS_CG_PARAM in the TRM.

Optional properties for the control loop parameters:
- nvidia,cg-scale: Boolean value, see the field DFLL_PARAMS_CG_SCALE in the TRM.

Required properties for I2C mode:
- nvidia,i2c-fs-rate: I2C transfer rate, if using full speed mode.

Example:

clock@70110000 {
        compatible = "nvidia,tegra124-dfll";
        reg = <0 0x70110000 0 0x100>, /* DFLL control */
              <0 0x70110000 0 0x100>, /* I2C output control */
              <0 0x70110100 0 0x100>, /* Integrated I2C controller */
              <0 0x70110200 0 0x100>; /* Look-up table RAM */
        interrupts = <GIC_SPI 62 IRQ_TYPE_LEVEL_HIGH>;
        clocks = <&tegra_car TEGRA124_CLK_DFLL_SOC>,
                 <&tegra_car TEGRA124_CLK_DFLL_REF>,
                 <&tegra_car TEGRA124_CLK_I2C5>;
        clock-names = "soc", "ref", "i2c";
        resets = <&tegra_car TEGRA124_RST_DFLL_DVCO>;
        reset-names = "dvco";
        #clock-cells = <0>;
        clock-output-names = "dfllCPU_out";
        vdd-cpu-supply = <&vdd_cpu>;
        status = "okay";

        nvidia,sample-rate = <12500>;
        nvidia,droop-ctrl = <0x00000f00>;
        nvidia,force-mode = <1>;
        nvidia,cf = <10>;
        nvidia,ci = <0>;
        nvidia,cg = <2>;

        nvidia,i2c-fs-rate = <400000>;
};