19572: cpu/stm32/periph_pwm: support of complementary timer outputs r=maribu a=gschorcht
### Contribution description
This PR provides the support of complementary timer outputs as PWM channels for advanced timers (TIM1/TIM8).
To use a complementary output of an advanced timer as PWM channel, the output is defined with an offset of 4, i.e. normal outputs are in the range of 0 to 3 (CH1...CH4) and complementary outputs are in the range of 4 to 6 (CH1N...CH3N). If the defined output is less than 4, the normal output is enabled, otherwise the complementary output is enabled.
This change is required to support PWM on boards that have connected the complementary outputs of advanced timers to the PWM connector pins, for example the STM32L496-DISCO board.
### Testing procedure
- Green CI
- Use any STM32 board which supports the `periph_pwm` feature. `tests/periph_pwm` should still work.
- Change the configuration for this board so that either timer TIM1 or TIM8 and a complementary channel is used for any exposed GPIO. `tests/periph_pwm` should also work with such a configuration.
### Issues/PRs references
Co-authored-by: Gunar Schorcht <gunar@schorcht.net>
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