dt-bindings: rtc: convert rtc-meson.txt to dt-schema

Convert the Amlogic Meson6 RTC bindings to dt-schema.

Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20221117-b4-amlogic-bindings-convert-v1-6-3f025599b968@linaro.org


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>