dt-bindings: irqchip: renesas-irqc: Document R-Car E3 support

Document support for the Interrupt Controller for External Devices
(INTC-EX) in the Renesas E3 (r8a77990) SoC.

No driver update is needed.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

Documentation/devicetree/bindings/interrupt-controller/renesas,irqc.txt

@@ -2,7 +2,8 @@ DT bindings for the R-Mobile/R-Car/RZ/G interrupt controller
 
 Required properties:
 
-- compatible: has to be "renesas,irqc-<soctype>", "renesas,irqc" as fallback.
+- compatible: must be "renesas,irqc-<soctype>" or "renesas,intc-ex-<soctype>",
+	      and "renesas,irqc" as fallback.
   Examples with soctypes are:
     - "renesas,irqc-r8a73a4" (R-Mobile APE6)
     - "renesas,irqc-r8a7743" (RZ/G1M)
@@ -19,6 +20,7 @@ Required properties:
     - "renesas,intc-ex-r8a77965" (R-Car M3-N)
     - "renesas,intc-ex-r8a77970" (R-Car V3M)
     - "renesas,intc-ex-r8a77980" (R-Car V3H)
+    - "renesas,intc-ex-r8a77990" (R-Car E3)
     - "renesas,intc-ex-r8a77995" (R-Car D3)
 - #interrupt-cells: has to be <2>: an interrupt index and flags, as defined in
   interrupts.txt in this directory