[PATCH] drm/amd: Drop abm_level property

[Xaver Hugl]

Like already mentioned in the power profiles daemon repository, I don't think 
this makes sense. This is a display setting, which compositors have interest 
in controlling, for example to:
- disable it in a bright environment, because afaiu it reduces the maximum 
screen brightness
- disable it when it shows color critical content
- disable it while profiling the display
- enable it when it shows content that's definitely not color critical (based 
on the content-type property of Wayland surfaces)
- enable it as a first step before properly dimming the screen on idle

If the primary concern here is that this hasn't been used by compositors and 
potential power savings aren't being realized, that could be solved by 
providing documentation about what the feature does in the kernel, and by 
sending a mail to wayland-devel describing why it should be used.

If the goal is to implement it in power profiles daemon and not get conflicts, I 
think disabling the property by default and instead enable it + disable the 
sysfs file when a CAP for it is set would make more sense than making the 
listed features impossible.