dt-bindings: mips: brcm: add Broadcom SoCs bindings

Add the yaml binding for MIPS Broadcom cable/DSL/settop platforms.

Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>