dt-bindings: arm: hisilicon: split the dt-bindings of each controller into a separate file

Split the devicetree bindings of each Hisilicon controller from
hisilicon.txt into a separate file, the file name is the compatible name
attach the .txt file name extension.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Link: https://lore.kernel.org/r/20200929141454.2312-4-thunder.leizhen@huawei.com
Signed-off-by: Rob Herring <robh@kernel.org>