drm/amd/powerplay: get overdrive clock and voltage information

Add sys interface to get overdrive clock and voltage information for
smu11.

Signed-off-by: Likun Gao <Likun.Gao@amd.com>
Reviewed-by: Kevin Wang <kevin1.wang@amd.com>
Reviewed-by: Evan Quan <evan.quan@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>