drm/radeon/dpm: Reenabling SS on Cayman

It reverts commit c745fe61 now that
Cayman is stable since VDDCI fix. Spread spectrum was not the culprit.

This depends on b0880e87


(drm/radeon/dpm: fix vddci setup typo on cayman).

Signed-off-by: Alexandre Demers <alexandre.f.demers@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org