dt-bindings: clocks: at91sam9x5-sckc: convert to yaml

Convert Atmel slow clock controller documentation to yaml.

Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230517094119.2894220-6-claudiu.beznea@microchip.com