ARM: dts: sun8i: Add NMI interrupt controller node

The NMI interrupt controller is in charge of the NMI pin exposed by
the SoC to the PMIC. The PMIC signals interrupts through this.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>