dt-bindings: arm: hisilicon: convert system controller bindings to json-schema

Convert the Hisilicon system controller and its variants binding to DT
schema format using json-schema. All of them are grouped into one yaml
file, to help users understand differences and avoid repeated
descriptions.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Link: https://lore.kernel.org/r/20200929141454.2312-11-thunder.leizhen@huawei.com
Signed-off-by: Rob Herring <robh@kernel.org>