robert-hh 9c7ad68165 mimxrt/machine_pwm: Start PWM only if freq and duty are set.
And also fix/improve the following:
- Simplify the duty handling a little bit.
- Allow duty_u16(65536), which sets the output high.
- Rename machine_pwm_start() to mp_machine_pwm_start(), in preparation for
  a possible start/stop method pair.
2023-05-04 13:09:39 +10:00
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