Document the top-level device tree binding for EcoNet MIPS-based SoCs. Signed-off-by: Caleb James DeLisle <cjd@cjdns.fr> Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org> Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>