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>