drm/amdgpu: delete pp_enable in adev

amdgpu not care powerplay or dpm is enabled.
just check ip functions and pp functions

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Rex Zhu <Rex.Zhu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>