dt-bindings: power: reset: gpio-restart: Convert to json-schema

Convert the GPIO restart bindings from the free-form text format to
json-schema.

Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20211217170042.2740058-1-thierry.reding@gmail.com