MSM device bandwidth device

devbw is a device that represents a MSM device's BW requirements from its
master port(s) to a different device's slave port(s) in a MSM SoC. This
device is typically used to vote for BW requirements from a device's (Eg:
CPU, GPU) master port(s) to the slave (Eg: DDR) port(s).

Required properties:
- compatible:		Must be "qcom,devbw"
- qcom,src-dst-ports:	A list of tuples where each tuple consists of a bus
			master port number and a bus slave port number.
- qcom,bw-tbl:		A list of meaningful instantaneous bandwidth values
			(in MB/s) that can be requested from the device
			master port to the slave port. The list of values
			depend on the supported bus/slave frequencies and the
			bus width.

Optional properties:
- qcom,active-only:	Indicates that the bandwidth votes need to be
			enforced only when the CPU subsystem is active.
- governor:		Initial governor to use for the device.
			Default: "performance"
- qcom,ab-percent:	Indicates a value in percent of instantaneous
			bandwidth which will be used to calculate the
			absolute/average bandwidth.

Example:

	qcom,cpubw {
		compatible = "qcom,devbw";
		qcom,src-dst-ports = <1 512>, <2 512>;
		qcom,active-only;
		qcom,bw-tbl =
			<  572 /*  75 MHz */ >,
			< 1144 /* 150 MHz */ >,
			< 1525 /* 200 MHz */ >,
			< 2342 /* 307 MHz */ >,
			< 3509 /* 460 MHz */ >,
			< 4684 /* 614 MHz */ >,
			< 6103 /* 800 MHz */ >,
			< 7102 /* 931 MHz */ >;
	};