dt-bindings: Introduce interconnect binding

This binding is intended to represent the relations between interconnect
controllers (providers) and consumer device nodes. It will allow creating
links between consumers and interconnect paths (exposed by interconnect
providers).

Reviewed-by: Evan Green <evgreen@chromium.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Georgi Djakov <georgi.djakov@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>