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

Memory controller is interconnected with memory clients and with the
External Memory Controller. Document new interconnect property which
turns memory controller into interconnect provider.
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20201104164923.21238-7-digetx@gmail.comSigned-off-by: Krzysztof Kozlowski <krzk@kernel.org>

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

@@ -16,6 +16,8 @@ Required properties:
   IOMMU specifier needed to encode an address. GART supports only a single
   address space that is shared by all devices, therefore no additional
   information needed for the address encoding.
+- #interconnect-cells : Should be 1. This cell represents memory client.
+  The assignments may be found in header file <dt-bindings/memory/tegra20-mc.h>.
 
 Example:
 	mc: memory-controller@7000f000 {
@@ -27,6 +29,7 @@ Example:
 		interrupts = <GIC_SPI 77 0x04>;
 		#reset-cells = <1>;
 		#iommu-cells = <0>;
+		#interconnect-cells = <1>;
 	};
 
 	video-codec@6001a000 {