dt-bindings: interrupt-controller: New binding for Meson-AXG SoC

Update the dt-binding documentation to support new compatible string
for the GPIO interrupt controller which found in Amlogic's Meson-AXG SoC.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Yixun Lan <yixun.lan@amlogic.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>