dt-bindings: input: gpio-beeper: Convert to yaml schema

Convert the bindings from plain text to yaml schema.

Signed-off-by: Fabio Estevam <festevam@denx.de>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Link: https://lore.kernel.org/r/20221120012135.2085631-1-festevam@gmail.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>