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

Add documentation for new optional properties in the exynos bus nodes:
interconnects, #interconnect-cells, samsung,data-clock-ratio.
These properties allow to specify the SoC interconnect structure which
then allows the interconnect consumer devices to request specific
bandwidth requirements.

Acked-by: Krzysztof Kozlowski <krzk@kernel.org>
Acked-by: Chanwoo Choi <cw00.choi@samsung.com>
Tested-by: Chanwoo Choi <cw00.choi@samsung.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Artur Świgoń <a.swigon@samsung.com>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>