pwm: Changes for v6.8-rc1

This contains a bunch of cleanups and simplifications across the board,
as well as a number of small fixes.

Perhaps the most notable change here is the addition of an API that
allows PWMs to be used in atomic contexts, which is useful when time-
critical operations are involved, such as using a PWM to generate IR
signals.

Finally, I have decided to step down as PWM subsystem maintainer. Due to
other responsibilities I have lately not been able to find the time that
the subsystem deserves and Uwe, who has been helping out a lot for the
past few years and has many things planned for the future, has kindly
volunteered to take over. I have no doubt that he will be a suitable
replacement.
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