dt-bindings: phy: tegra-xusb: Convert to json-schema

Convert the Tegra XUSB pad controller bindings from free-form text
format to json-schema.
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://lore.kernel.org/r/20230113150804.1272555-1-thierry.reding@gmail.comSigned-off-by: Vinod Koul <vkoul@kernel.org>