arm64: dts: NS2: Add all of the UARTs

Add all of the UARTs present on NS2 and enable them in the SVK device
tree file.  Also, do some magic to make sure that uart3 is discovered as
ttyS0 (as that is the console UART).

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