dt-bindings: phy: convert phy-hi3660-usb3.txt to yaml

Convert Hisilicon Kirin 960 USB3 PHY bindings to DT schema
format using json-schema.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/edfeafe6b5a60a84d08095fb380f32e61af46d40.1599206213.git.mchehab+huawei@kernel.org


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