ARM: brcmstb: dts: add a reference DTS for Broadcom 7445

Add a sample DTS which will allow bootup of a board populated
with the BCM7445 chip.

Signed-off-by: Marc Carino <marc.ceeeee@gmail.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Cc: Matt Porter <mporter@linaro.org>
Signed-off-by: Matt Porter <mporter@linaro.org>