dt-bindings: devfreq: Add documentation for the interconnect properties

- exynos,saturation-ratio: the percentage value which is used to calibrate

			the performance count against total cycle count.

Optional properties for the interconnect functionality (QoS frequency

constraints):

- #interconnect-cells: should be 0.

- interconnects: as documented in ../interconnect.txt, describes a path at the

  higher level interconnects used by this interconnect provider.

  If this interconnect provider is directly linked to a top level interconnect

  provider the property contains only one phandle. The provider extends

  the interconnect graph by linking its node to a node registered by provider

  pointed to by first phandle in the 'interconnects' property.

- samsung,data-clock-ratio: ratio of the data throughput in B/s to minimum data

   clock frequency in Hz, default value is 8 when this property is missing.

Detailed correlation between sub-blocks and power line according to Exynos SoC:

- In case of Exynos3250, there are two power line as following:

	VDD_MIF |--- DMC

		devfreq = <&bus_leftbus>;

		status = "okay";

	};

Example 3:

	An interconnect path "bus_display -- bus_leftbus -- bus_dmc" on

	Exynos4412 SoC with video mixer as an interconnect consumer device.

	soc {

		bus_dmc: bus_dmc {

			compatible = "samsung,exynos-bus";

			clocks = <&clock CLK_DIV_DMC>;

			clock-names = "bus";

			operating-points-v2 = <&bus_dmc_opp_table>;

			samsung,data-clock-ratio = <4>;

			#interconnect-cells = <0>;

		};

		bus_leftbus: bus_leftbus {

			compatible = "samsung,exynos-bus";

			clocks = <&clock CLK_DIV_GDL>;

			clock-names = "bus";

			operating-points-v2 = <&bus_leftbus_opp_table>;

			#interconnect-cells = <0>;

			interconnects = <&bus_dmc>;

		};

		bus_display: bus_display {

			compatible = "samsung,exynos-bus";

			clocks = <&clock CLK_ACLK160>;

			clock-names = "bus";

			operating-points-v2 = <&bus_display_opp_table>;

			#interconnect-cells = <0>;

			interconnects = <&bus_leftbus &bus_dmc>;

		};

		bus_dmc_opp_table: opp_table1 {

			compatible = "operating-points-v2";

			/* ... */

		}

		bus_leftbus_opp_table: opp_table3 {

			compatible = "operating-points-v2";

			/* ... */

		};

		bus_display_opp_table: opp_table4 {

			compatible = "operating-points-v2";

			/* .. */

		};

		&mixer {

			compatible = "samsung,exynos4212-mixer";

			interconnects = <&bus_display &bus_dmc>;

			/* ... */

		};

	};