arm: dts: san*: Fix compatible string for rtc-pcf8563

Update a compatible string in the "rtc" node for all SAN boards.
The device uses an out-of-tree driver with SECO specific changes.
A new compatible ID can be found in the source code of the driver [1].

Links:
[1] https://git.seco.com/seco-ne/yocto/layers/meta-seconorth-machine/-/blob/11c61f6430542b0516a6446d0585526fc1eed86c/recipes-kernel/modules/rtc-pcf8563-guf/rtc-pcf8563-guf.c#L618



Signed-off-by: Dmitry Petrov <dmitry.petrov@rtsoft.de>