dt-bindings: stm32: add STM32MP21 and STM32MP23 compatibles for syscon

Add the new syscon compatibles for STM32MP21 syscfg = "st,stm32mp21-syscfg"
and for STM32MP23 syscfg = "st,stm32mp23-syscfg".

Signed-off-by: Amelie Delaunay <amelie.delaunay@foss.st.com>
Acked-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://lore.kernel.org/r/20250225-b4-stm32mp2_new_dts-v2-4-1a628c1580c7@foss.st.com


Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>