dt-bindings: memory: tegra20: emc: Document new interconnect property

External Memory Controller is interconnected with memory controller and
with external memory. Document new interconnect property which turns EMC
into interconnect provider.
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20201104164923.21238-8-digetx@gmail.comSigned-off-by: Krzysztof Kozlowski <krzk@kernel.org>

Documentation/devicetree/bindings/memory-controllers/nvidia,tegra20-emc.txt

@@ -13,6 +13,7 @@ Properties:
 - interrupts : Should contain EMC General interrupt.
 - clocks : Should contain EMC clock.
 - nvidia,memory-controller : Phandle of the Memory Controller node.
+- #interconnect-cells : Should be 0.
 
 Child device nodes describe the memory settings for different configurations and clock rates.
 
@@ -21,6 +22,7 @@ Example:
 	memory-controller@7000f400 {
 		#address-cells = < 1 >;
 		#size-cells = < 0 >;
+		#interconnect-cells = <0>;
 		compatible = "nvidia,tegra20-emc";
 		reg = <0x7000f400 0x400>;
 		interrupts = <0 78 0x04>;