arm: dts: Import device tree for Broadcom Northstar

This brings in the main SoC device tree used by the
Broadcom Northstar chipset, i.e. BCM4709x and BCM5301x.
This is taken from the v6.3 Linux kernel.

Cc: Rafał Miłecki <rafal@milecki.pl>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>