dt-bindings: ps2-gpio: convert binding to json-schema

Convert the ps2-gpio dt-binding documentation to DT schema format using
the json-schema.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Signed-off-by: Danilo Krummrich <danilokrummrich@dk-develop.de>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220529132638.13420-1-danilokrummrich@dk-develop.de