dt-bindings: mfd: syscon: add some compatible strings for Hisilicon

Add some compatible strings for Hisilicon controllers:
hisilicon,hi6220-sramctrl  --> Hi6220 SRAM controller
hisilicon,pcie-sas-subctrl --> HiP05/HiP06 PCIe-SAS subsystem controller
hisilicon,peri-subctrl     --> HiP05/HiP06 PERI subsystem controller
hisilicon,dsa-subctrl      --> HiP05/HiP06 DSA subsystem controller

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Link: https://lore.kernel.org/r/20200929141454.2312-2-thunder.leizhen@huawei.com
[robh: sort entries alphabetically]
Signed-off-by: Rob Herring <robh@kernel.org>