drm/amd/powerplay: add od condition for power limit

Add condition to judge whether overdrive is enabled and correct power
limit value for overdrive used by power limit interface.

Signed-off-by: Likun Gao <Likun.Gao@amd.com>
Reviewed-by: Kevin Wang <kevin1.wang@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>