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.
- operating-points-v2:	A phandle to the OPP v2 table that holds 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,ddr-type:	Optional property indicates ddr type which can support
				different frequencies for a given target.

Example:

	bw_opp_table: bw-opp-table {
		compatible = "operating-points-v2";
		opp-75  {
			opp-hz = /bits/ 64 <  572 >; /*  75 MHz */
		};
		opp-150 {
			opp-hz = /bits/ 64 < 1144 >; /* 150 MHz */
		};
		opp-200 {
			opp-hz = /bits/ 64 < 1525 >; /* 200 MHz */
		};
		opp-307 {
			opp-hz = /bits/ 64 < 2342 >; /* 307 MHz */
		};
		opp-460 {
			opp-hz = /bits/ 64 < 3509 >; /* 460 MHz */
		};
		opp-614 {
			opp-hz = /bits/ 64 < 4684 >; /* 614 MHz */
		};
		opp-800 {
			opp-hz = /bits/ 64 < 6103 >; /* 800 MHz */
		};
		opp-931 {
			opp-hz = /bits/ 64 < 7102 >; /* 931 MHz */
		};
	};
	qcom,cpubw {
		compatible = "qcom,devbw";
		qcom,src-dst-ports = <1 512>, <2 512>;
		qcom,active-only;
		operating-points-v2 = <&bw_opp_table>;
		ddr3-opp {
			operating-points-v2 = <&ddr3_bw_opp_table>;
			qcom,ddr-type = <DDR_TYPE_LPDDR3>;
		};
		ddr4-opp {
			operating-points-v2 = <&ddr4_bw_opp_table>;
			qcom,ddr-type = <DDR_TYPE_LPDDR4X>;
		};
	};