dt-bindings: irq: arm,versatile-fpga: add compatible string for OX810SE SoC

Under the OX810SE, this same controller is used as "Reference Peripheral
Specification" Interrupt Controller, so add new compatible string to support
the Oxford Semiconductor OX810SE SoC Interrupt Controller.
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>

Documentation/devicetree/bindings/interrupt-controller/arm,versatile-fpga-irq.txt

@@ -6,7 +6,7 @@ controllers are OR:ed together and fed to the CPU tile's IRQ input. Each
 instance can handle up to 32 interrupts.
 
 Required properties:
-- compatible: "arm,versatile-fpga-irq"
+- compatible: "arm,versatile-fpga-irq" or "oxsemi,ox810se-rps-irq"
 - interrupt-controller: Identifies the node as an interrupt controller
 - #interrupt-cells: The number of cells to define the interrupts.  Must be 1
   as the FPGA IRQ controller has no configuration options for interrupt