dt-bindings: gpio: omap: Convert to json-schema

Convert the OMAP GPIO Device Tree binding documentation to json-schema.
The GPIO hogs node names defined to end with a 'hog' suffix.

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>