dt-bindings: interrupt-controller: New binding for Meson-G12A SoC

Update the dt-binding document to support new compatible string for the
GPIO interrupt controller which found in Amlogic's Meson-G12A SoC.

Signed-off-by: Xingyu Chen <xingyu.chen@amlogic.com>
Signed-off-by: Jianxin Pan <jianxin.pan@amlogic.com>
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>