if max od engine clock limit and memory clock limit are not set
in vbios. driver will allow underclocking instand of disable od feature
completely.
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>