dt-bindings: IDU-intc: Add support for edge-triggered interrupts

This updates the documentation for supporting an optional extra interrupt
cell to specify edge vs level triggered.
Signed-off-by: Mischa Jonker <mischa.jonker@synopsys.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

Documentation/devicetree/bindings/interrupt-controller/snps,archs-idu-intc.txt

@@ -8,11 +8,20 @@ Properties:
 
 - compatible: "snps,archs-idu-intc"
 - interrupt-controller: This is an interrupt controller.
-- #interrupt-cells: Must be <1>.
-
-  Value of the cell specifies the "common" IRQ from peripheral to IDU. Number N
-  of the particular interrupt line of IDU corresponds to the line N+24 of the
-  core interrupt controller.
+- #interrupt-cells: Must be <1> or <2>.
+
+  Value of the first cell specifies the "common" IRQ from peripheral to IDU.
+  Number N of the particular interrupt line of IDU corresponds to the line N+24
+  of the core interrupt controller.
+
+  The (optional) second cell specifies any of the following flags:
+    - bits[3:0] trigger type and level flags
+        1 = low-to-high edge triggered
+        2 = NOT SUPPORTED (high-to-low edge triggered)
+        4 = active high level-sensitive <<< DEFAULT
+        8 = NOT SUPPORTED (active low level-sensitive)
+  When no second cell is specified, the interrupt is assumed to be level
+  sensitive.
 
   The interrupt controller is accessed via the special ARC AUX register
   interface, hence "reg" property is not specified.