dt-bindings: clock: Add RTC related clocks for Ingenic SoCs.

Add RTC related clocks bindings for the JZ4780 SoC, the X1000 SoC,
and the X1830 SoC from Ingenic.

Tested-by: 周正 (Zhou Zheng) <sernia.zhou@foxmail.com>
Signed-off-by: 周琰杰 (Zhou Yanjie) <zhouyanjie@wanyeetech.com>
Link: https://lore.kernel.org/r/20200725051136.58220-2-zhouyanjie@wanyeetech.com


Signed-off-by: Stephen Boyd <sboyd@kernel.org>