Adreno Power Levels

The Adreno GPU definition should include a variable number of power levels
defining the GPU and bus frequencies for the levels that the GPU can operate at.

Required properties:

- compatible:	The compatible name for the object (qcom,gpu-pwrlevels)

Each powerlevel definition is as follows:

- reg:              Index of the power level (lower is considered higher
		    performance)
- qcom,gpu-freq:    The GPU frequency for the power level (in HZ)
- qcom,bus-freq:    An index representing the bus scaling usecase appropriate
		    for the power level
- qcom,io-fraction: A number indicating the fraction of the CPU I/O busy that
		    this operating point should represent.

Sample usage:

qcom,kgsl-3d0@fdb00000 {
	...
	qcom,gpu-pwrlevels {
		#address-cells = <1>;
		#size-cells = <0>;

		compatible = "qcom,gpu-pwrlevels";

		qcom,gpu-pwrlevel@0 {
			reg = <0>;
			qcom,gpu-freq = <5000000000>;
			qcom,bus-freq = <3>;
			qcom,io_fraction = <0>;
		};
	};

	...
};