arm64: hip05-d02: Document devicetree bindings for Hisilicon Hip05-D02 Board

This patch adds documentation for the devicetree bindings used by the
DT files of Hisilicon Hip05-D02 development board.

Signed-off-by: Ding Tianhong <dingtianhong@huawei.com>
Signed-off-by: Wei Xu <xuwei5@hisilicon.com>