dt-bindings: PCI: kirin: Add support for Kirin970

Add a new compatible, plus the new bindings needed by
HiKey970 board.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/875a4571e253040d3885ee1f37467b0bade7361b.1628061310.git.mchehab+huawei@kernel.org


Signed-off-by: Rob Herring <robh@kernel.org>