Documentation: add Device tree bindings for Hisilicon hip04 ethernet

This patch adds the Device Tree bindings for the Hisilicon hip04
Ethernet controller, including 100M / 1000M controller.

Signed-off-by: Zhangfei Gao <zhangfei.gao@linaro.org>
Signed-off-by: Ding Tianhong <dingtianhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>