arm64: dts: st: set RIFSC as an access controller on stm32mp21x platforms

arm64: dts: st: set RIFSC as an access controller on stm32mp21x platforms

Similarly to stm32mp23x/25x platforms, the RIFSC is a firewall
controller. Declare it as an access controller, keep the "simple-bus"
compatible in case CONFIG_STM32_FIREWALL is not set and update the
child nodes.

Signed-off-by: Gatien Chevallier <gatien.chevallier@foss.st.com>
Link: https://lore.kernel.org/r/20251106-rifsc_debugfs-v2-2-f90e94ae756d@foss.st.com
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>