Devfreq simple device

devfreq-simple-dev is a device that represents a simple device that cannot do
any status reporting and uses a clock that can be scaled by one of more
devfreq governors.  It provides a list of usable frequencies for the device
and some additional optional parameters.

Required properties:
- compatible:		Must be "devfreq-simple-dev"
- clock-names:		Must be "devfreq_clk"
- clocks:		Must refer to the clock that's fed to the device.
Optional properties:
- polling-ms:	Polling interval for the device in milliseconds. Default: 50
- governor:	Initial governor to user for the device. Default: "performance"
- qcom,prepare-clk:	Prepare the device clock during initialization.
- freq-tbl-khz:		A list of usable frequencies (in kHz) for the device
			clock.

Example:

	qcom,cache {
		compatible = "devfreq-simple-dev";
		clock-names = "devfreq_clk";
		clocks = <&clock_krait clk_l2_clk>;
		polling-ms = 50;
		governor = "cpufreq";
		freq-tbl-khz =
			<  300000 >,
			<  345600 >,
			<  422400 >,
			<  499200 >,
			<  576000 >,
			<  652800 >,
			<  729600 >,
			<  806400 >,
			<  883200 >,
			<  960000 >,
			< 1036800 >,
			< 1113600 >,
			< 1190400 >,
			< 1267200 >,
			< 1344000 >,
			< 1420800 >,
			< 1497600 >,
			< 1574400 >,
			< 1651200 >,
			< 1728000 >;
	};