ARM: dts: sun8i: Cleanup the Pinecube AXP209 node

This fixes a few things with the Pinecube AXP209 node:
- No compatible is required since it is using an AXP209 (not AXP203)
  according to the schematics and this is what the included axp209.dtsi
  already has;
- The interrupt-controller and #interrupt-cells properties are already
  described in the included axp209.dtsi;
- The interrupt comes through the NMI controller, not directly through
  the GIC.

Signed-off-by: Paul Kocialkowski <contact@paulk.fr>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20201206165131.1041983-4-contact@paulk.fr