mfd: stm32-timers: Add support for interrupts

mfd: stm32-timers: Add support for interrupts

There are two types of STM32 timers that may have:

- a global interrupt line
- 4 dedicated interrupt lines.

Those interrupts are optional as defined in the dt-bindings. Enforce checks
on either one, four or no interrupts are provided with their names.
Optionally get them here, to be used by child devices.

Signed-off-by: Fabrice Gasnier <fabrice.gasnier@foss.st.com>
Link: https://lore.kernel.org/r/20230829134029.2402868-5-fabrice.gasnier@foss.st.com
Signed-off-by: Lee Jones <lee@kernel.org>