drm/amd/powerplay: support enabled ppfeatures retrieving and setting V3

User can use "ppfeatures" sysfs interface to retrieve and set enabled
powerplay features.

V2: expose this feature for Vega10 and later dGPUs
V3: squash in removal of unused variable (Alex)

Signed-off-by: Evan Quan <[email protected]>
Reviewed-by: Alex Deucher <[email protected]>
Signed-off-by: Alex Deucher <[email protected]>
6 files changed