board: Add new Broadcom Northstar board

This adds a simple Northstar "BRCMNS" board to be used with
the BCM4708x and BCM5301x chips.

The main intention is to use this with the D-Link DIR-890L
and DIR-885L routers for loading the kernel into RAM from
NAND memory using the BCH-1 ECC and using the separately
submitted SEAMA load command, so we are currently not adding
support for things such as networking.

The DTS file is a multiplatform NorthStar board, designed to
be usable with several NorthStar designs by avoiding any
particulars not related to the operation of U-Boot.

If other board need other ECC for example, they need to
create a separate DTS file and augment the code, but I don't
know if any other users will turn up.

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