dt-bindings: tegra186-pmc: Add interrupt controller properties

The PMC can be a top-level interrupt controller that provides the top-
level controls for wake events. Add optional properties to mark the PMC
as interrupt controller.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>

Documentation/devicetree/bindings/arm/tegra/nvidia,tegra186-pmc.txt

@@ -15,6 +15,9 @@ Required properties:
 
 Optional properties:
 - nvidia,invert-interrupt: If present, inverts the PMU interrupt signal.
+- interrupt-controller: Identifies the node as an interrupt controller.
+- #interrupt-cells: Specifies the number of cells needed to encode an
+  interrupt source. The value must be 2.
 
 Example: