dt-bindings: display: tegra: Convert to json-schema

Convert the Tegra host1x controller bindings from the free-form text
format to json-schema.

This also adds the missing display-hub DT bindings that were not
previously documented.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>