drm/amd/amdgpu: Comment out currently unused SI DPM struct

The tahiti_le structure is not currently used.  Comment it out
to avoid warnings.

Signed-off-by: Tom St Denis <tom.stdenis@amd.com>
Acked-by: Edward O'Callaghan <funfunctor@folklore1984.net>
Reviewed-by: Huang Rui <ray.huang@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>