arm64: dts: st: add timer pins for stm32mp257f-ev1

arm64: dts: st: add timer pins for stm32mp257f-ev1

Add timer pins available on stm32mp257f-ev1, configured for PWM:
- timer3 CH2 is available on mikroBUS connector
- timer8 CH1, timer8 CH4, timer10 CH1 and timer12 CH2 are available
  on EXPANSION connector
Arbitrary define all these pins to be used as PWM (output) channels,
except for timer10 CH1, to be used as counter input.

Signed-off-by: Fabrice Gasnier <fabrice.gasnier@foss.st.com>
Link: https://lore.kernel.org/r/20250110091922.980627-8-fabrice.gasnier@foss.st.com
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>