watchdog: dt-bindings: atmel,at91sam9-wdt: convert to json-schema

Convert at91sam9 WDT binding for Atmel/Microchip SoCs to json-schema
format.

Signed-off-by: Sergiu Moga <sergiu.moga@microchip.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20220714125122.144377-1-sergiu.moga@microchip.com


Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>