dt-bindings: interrupt-controller: New binding for Meson-A1 SoCs

Update dt-binding document for GPIO interrupt controller of Meson-A1 SoCs

Signed-off-by: Qianggui Song <qianggui.song@amlogic.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20191216123645.10099-2-qianggui.song@amlogic.com