arm64: dts: st: Add PCIe Root Complex mode on stm32mp251

arm64: dts: st: Add PCIe Root Complex mode on stm32mp251

Add pcie_rc node to support STM32 MP25 PCIe driver based on the
DesignWare PCIe core configured as Root Complex mode

Supports Gen1/Gen2, single lane, MSI interrupts using the ARM GICv2m

Signed-off-by: Christian Bruel <christian.bruel@foss.st.com>
Acked-by: Manivannan Sadhasivam <mani@kernel.org>
Link: https://lore.kernel.org/r/20250820075411.1178729-10-christian.bruel@foss.st.com
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>