dt-bindings: PCI: dwc: rockchip: Add missing legacy-interrupt-controller

Rockchip RK356x and RK3588 handle legacy interrupts via a ganged
interrupts. The RK356x DT implements this via a sub-node named
"legacy-interrupt-controller", just like a couple of other PCIe
implementations. This adds proper documentation for this and updates
the example to avoid regressions.
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Link: https://lore.kernel.org/r/20230731165723.53069-5-sebastian.reichel@collabora.comSigned-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/pci/rockchip-dw-pcie.yaml

@@ -93,6 +93,28 @@ properties:
       - const: legacy
       - const: err
 
+  legacy-interrupt-controller:
+    description: Interrupt controller node for handling legacy PCI interrupts.
+    type: object
+    additionalProperties: false
+    properties:
+      "#address-cells":
+        const: 0
+
+      "#interrupt-cells":
+        const: 1
+
+      interrupt-controller: true
+
+      interrupts:
+        items:
+          - description: combined legacy interrupt
+    required:
+      - "#address-cells"
+      - "#interrupt-cells"
+      - interrupt-controller
+      - interrupts
+
   msi-map: true
 
   num-lanes: true
@@ -180,6 +202,14 @@ examples:
             reset-names = "pipe";
             #address-cells = <3>;
             #size-cells = <2>;
+
+            legacy-interrupt-controller {
+                interrupt-controller;
+                #address-cells = <0>;
+                #interrupt-cells = <1>;
+                interrupt-parent = <&gic>;
+                interrupts = <GIC_SPI 72 IRQ_TYPE_EDGE_RISING>;
+            };
         };
     };
 ...