arm: stm32mp2: add multifunction timer support for stm32mp25

arm: stm32mp2: add multifunction timer support for stm32mp25

Add support for STM32MP25 SoC.
Identification and hardware configuration registers allow to read the
timer version and capabilities (counter width, ...).
So, rework the probe to avoid touching ARR register by simply read the
counter width when available. This may avoid messing with a possibly
running timer.
Also add useful bit fields to stm32-timers header file.

Signed-off-by: Cheick Traore <cheick.traore@foss.st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>