arm64: dts: st: Adjust interrupt-controller for stm32mp21 SoCs

Use gic-400 compatible for aarch64

Fixes: 7a57b1bb ("arm64: dts: st: introduce stm32mp21 SoCs family")
Signed-off-by: Christian Bruel <christian.bruel@foss.st.com>
Link: https://lore.kernel.org/r/20250415111654.2103767-4-christian.bruel@foss.st.com


Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>