dt-bindings: rtc: Add Amlogic A4 and A5 RTC

Add documentation describing the Amlogic A4(A113L2) and A5(A113X2) RTC.

Signed-off-by: Yiting Deng <yiting.deng@amlogic.com>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Xianwei Zhao <xianwei.zhao@amlogic.com>
Link: https://lore.kernel.org/r/20241112-rtc-v6-1-a71b60d2f354@amlogic.com


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