This commit adds the device tree bindings description for Amlogic's GPIO
interrupt controller available on the meson8b, gxbb and gxl SoC families

Cc: Heiner Kallweit <hkallweit1@gmail.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>