The V3s/V3 has a NMI interrupt controller, mainly used for the AXP209.
Its address follows the system controller block, which was previously
incorrectly described as spanning over 0x1000 address bytes.
Even though this is what the Allwinner documentation indicates,
precedence from other SoCs such as the R40 suggests that this is not
actually the case.

This reduces the system controller address span up to the NMI
controller and adds a node for the controller, with its dedicated
compatible.

While the interrupt number was found in Allwinner's documentation,
the address for the controller is specified in any Allwinner SDK
supporting sun8iw8 (V3/V3s) at:
drivers/power/axp_power/axp20/axp20-board.c

It was tested to work on a V3 board with an AXP209 connected to the
NMI interrupt line.
Signed-off-by: Paul Kocialkowski <contact@paulk.fr>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20201206165131.1041983-3-contact@paulk.fr