dt-bindings: interrupt-controller: realtek,rtl-intc: Allow 2 interrupt cells

The Realtek Otto SoC interrupt controller supports hardware interrupt
routing to multiple parent CPU interrupt lines. To utilize this
multi-domain support, peripheral devices need a way to explicitly
specify their desired parent interrupt line in the device tree.

Update the "#interrupt-cells" property to accept either 1 or 2 cells.

 1 cell:  Specifies the hardware interrupt index, implicitly routing it
     	  to the first available parent (maintaining backward compatibility).

 2 cells: The first cell specifies the hardware interrupt index and
          the second cell specifies the targeted parent interrupt index.

Signed-off-by: Markus Stockhausen <markus.stockhausen@gmx.de>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://patch.msgid.link/20260605211646.2101652-2-markus.stockhausen@gmx.de

Documentation/devicetree/bindings/interrupt-controller/realtek,rtl-intc.yaml

@@ -32,8 +32,9 @@ properties:
 
   "#interrupt-cells":
     description:
-      SoC interrupt line index.
-    const: 1
+      First cell is the SoC interrupt line index. Optional second cell
+      specifies the parent interrupt index to route to.
+    enum: [1, 2]
 
   reg:
     minItems: 1