dt-bindings: rtc: st,stm32-rtc: Make each example a separate entry

Each independent example should be a separate entry. This allows for
'interrupts' to have different cell sizes.

Signed-off-by: Rob Herring <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

Documentation/devicetree/bindings/rtc/st,stm32-rtc.yaml

···
       st,syscfg = <&pwrcfg 0x00 0x100>;
     };
 
+  - |
     #include <dt-bindings/interrupt-controller/arm-gic.h>
     #include <dt-bindings/clock/stm32mp1-clks.h>
     rtc@5c004000 {