Navio2 exports its leds via /sys/class/leds interface. We reuse it in
order not to conflict with GPIO_Sysfs. Otherwise we'd get a Device Busy
error in GPIO_Sysfs::_export_pin().
pwm backend to drive leds.
In new Disco releases, the led sysfs api will replace the pwm sysfs
api to drive the tricolor led.
Keep pwm sysfs api for compatibility reasons.
Georgii Staroselskii
Randy Mackay
Lucas De Marchi
Mathieu OTHACEHE