arm64: dts: rockchip: add rtc to rock3a

Add devicetree node for hym8563 rtc to
Radxa ROCK3 Model A board.

Signed-off-by: Chukun Pan <amadeus@jmu.edu.cn>
Link: https://lore.kernel.org/r/20220726023046.5876-1-amadeus@jmu.edu.cn


Signed-off-by: Heiko Stuebner <heiko@sntech.de>