dt-bindings: arm: tegra: Document #reset-cells property of the Tegra20 MC

Memory Controller has a memory client "hot reset" functionality, which
resets the DMA interface of a memory client, so MC is a reset controller.
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>

Documentation/devicetree/bindings/arm/tegra/nvidia,tegra20-mc.txt

@@ -6,11 +6,21 @@ Required properties:
   example below. Note that the MC registers are interleaved with the
   GART registers, and hence must be represented as multiple ranges.
 - interrupts : Should contain MC General interrupt.
+- #reset-cells : Should be 1. This cell represents memory client module ID.
+  The assignments may be found in header file <dt-bindings/memory/tegra20-mc.h>
+  or in the TRM documentation.
 
 Example:
-	memory-controller@7000f000 {
+	mc: memory-controller@7000f000 {
 		compatible = "nvidia,tegra20-mc";
 		reg = <0x7000f000 0x024
 		       0x7000f03c 0x3c4>;
 		interrupts = <0 77 0x04>;
+		#reset-cells = <1>;
+	};
+
+	video-codec@6001a000 {
+		compatible = "nvidia,tegra20-vde";
+		...
+		resets = <&mc TEGRA20_MC_RESET_VDE>;
 	};