Add device tree files for Broadcom Northstar based SVKs.  Since the
bcm5301x.dtsi already exists, all that is necessary is the dts files to
enable the UARTs.  With these files, the SVKs are able to boot to shell.
Signed-off-by: Jon Mason <jonmason@broadcom.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>