drm/amd/powerplay: Update CKS on/ CKS off voltage offset calculation

CKS on/off voltage offset calculation algorithm takes in a few coefficients.
We need to update them for polaris to latest coefficients to align with BB.

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