ARM: dts: NSP: Add Ax stepping modifications

While uncommon, some Ax NSP SoCs exist in the wild. This stepping
requires a modified secondary CPU boot-reg and removal of DMA coherency
properties. Without these modifications, the secondary CPU will be
inactive and many peripherals will exhibit undefined behaviour.

Signed-off-by: Matthew Hagan <mnhagan88@gmail.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>