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: NRob Herring <robh@kernel.org>
Signed-off-by: NYixun Lan <yixun.lan@amlogic.com>
Signed-off-by: NMarc Zyngier <marc.zyngier@arm.com>

Documentation/devicetree/bindings/interrupt-controller/amlogic,meson-gpio-intc.txt

@@ -14,6 +14,7 @@ Required properties:
     "amlogic,meson8b-gpio-intc" for meson8b SoCs (S805) or
     "amlogic,meson-gxbb-gpio-intc" for GXBB SoCs (S905) or
     "amlogic,meson-gxl-gpio-intc" for GXL SoCs (S905X, S912)
+    "amlogic,meson-axg-gpio-intc" for AXG SoCs (A113D, A113X)
 - interrupt-parent : a phandle to the GIC the interrupts are routed to.
    Usually this is provided at the root level of the device tree as it is
    common to most of the SoC.