Read PWM config from /boot/firmware first to support Bookworm and later OSes

[thatcomputerguy0101]

Starting in RPiOS Bookworm, the boot partition mount point moved from /boot to /boot/firmware. Due to this, config.txt is now located at /boot/firmware/config.txt for modern RPiOS versions. This change set searches the new location first, falling back to the old location if an IOException occurs (the new file is not found).

[thatcomputerguy0101]

On second thought, it may be better to extract the PWM pin configuration from running pinctrl instead, since that will always report the active configuration. The current implementation might report the wrong values if the pwm dtoverlay line appears in a conditional block of config.txt.

[thatcomputerguy0101]

pinctrl is backed by gpiolib which is probably more appropriate for reading the current configuration. (It also allows changing the alternate functions dynamically, but at risk of conflict with the kernel.) gpiolib also has mechanisms for getting the physical pin layout, which could act as a fallback for missing board layouts.

[thatcomputerguy0101]

Actually, I'm probably mixing up libraries here. gpiolib is what the gpio character device api is supposed to supersede.

[mattjlewis]

Thank you - merged