dts: arm: st: stm32mp25*_m33.dtsi: add init dtsi

Add the initial device tree source include (dtsi) files for the
stm32mp25 series boards, covering non-secure configuration for zephyr on
the Cortex-M33 core.
These files provide the basic hardware description, including CPU
(Cortex-M33), memory, RCC clock controller and NVIC interrupt
controller.

Key features:
- Set flash and RAM addresses to DDR memory.
- Adjust RCC peripheral address for non-secure context.

Signed-off-by: Youssef Zini <youssef.zini@savoirfairelinux.com>