Set backlight to hard coded intensity on wakeup (and set repeatedly) for macOS High Sierra

[andywarduk]

I have added a dirty hack in my fork of AMDGPUWakeHandler to force the backlight intensity on wakeup for macOS High Sierra. Setting the intensity once didn't work - I assume something else is resetting it after we tried. There's a dirty 10 second loop in there which sets the intensity every 0.5 seconds.

[blackgate]

@andywarduk I've updated the kext. The update enables the GMUX interrupts when waking up from sleep the same way linux does in its "apple-gmux" implementation. Please check if the new version solves your problem.