ARM: dts: NSP: Add and enable amac2

Add and enable the third AMAC ethernet interface in the device trees for
the platforms where it is present.  Also, enable amac1 on some of the
platforms where that was missing.

Signed-off-by: Jon Mason <jon.mason@broadcom.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>