arm64: dts: st: add low-power timer nodes on stm32mp251

arm64: dts: st: add low-power timer nodes on stm32mp251

Add low-power timer (LPTimer) support on STM32MP25 SoC.
The full feature set is implemented in LPTIM1/2/3/4. LPTIM5 supports a
smaller set of features (no capture/compare) channel. Still, LPTIM5 can
be used as single PWM, counter, trigger or timer.

Signed-off-by: Fabrice Gasnier <fabrice.gasnier@foss.st.com>
Link: https://lore.kernel.org/r/20250429125133.1574167-7-fabrice.gasnier@foss.st.com
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>