ARM: dts: meson8: enable the GPIO interrupt controller

This enables the GPIO interrupt controller for the Meson8 SoCs.
Interrupt support on the GPIOs can be used by the MMC framework to
detect when an SD card is inserted/removed or by the input framework to
detect button presses.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>