iio: trigger: stm32-timer: add support for stm32mp25

iio: trigger: stm32-timer: add support for stm32mp25

Add support for STM32MP25 SoC. Use newly introduced compatible to handle
this new HW variant. Add TIM20 trigger definitions that can be used by
the stm32 analog-to-digital converter. Use compatible data to identify
it.
As the counter framework is now superseding the deprecated IIO counter
interface (IIO_COUNT), don't support it. Only register IIO trigger
devices for ADC usage. So, make the valids_table a cfg option.

Signed-off-by: Fabrice Gasnier <fabrice.gasnier@foss.st.com>
Link: https://patch.msgid.link/20241220095927.1122782-4-fabrice.gasnier@foss.st.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>