drm/amd/pp: Change activity_target for performance optimization on Polaris

And not support perDPM level optimization on Polaris, so
delete sclk activity_target array.

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>