drm/amdgpu/pm: only hide average power on SI and pre-RENOIR APUs

We can get this on RENOIR and newer via the SMU metrics
table.

Reviewed-by: Evan Quan <evan.quan@amd.com>
Acked-by: Nirmoy Das <nirmoy.das@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>