ARM: meson: enable MESON_IRQ_GPIO also for MACH_MESON8

Now that the GPIO interrupt controller also supports the Meson8 SoCs we
can enable it via Kconfig.

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