ARM: dts: stm32: phycore-stm32mp15: Disable optional SoM peripherals

ARM: dts: stm32: phycore-stm32mp15: Disable optional SoM peripherals

Following peripherals are optional on phyCORE-STM32MP15x following
PHYTEC standard SoM variants: external RTC, EEPROM, SPI NOR.
Also NAND (fmc) can be populated instead of eMMC (sdmmc2).

So disable those peripherals on SoM dtsi file and enable them on board
dts file.
Additionally, enable by default the "DTS" SoC IP on common SoM dtsi file
as it is not an optional IP in STM32MP15x SoC.

Signed-off-by: Christophe Parant <c.parant@phytec.fr>
Link: https://lore.kernel.org/r/20251210101611.27008-10-c.parant@phytec.fr
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>