drm/amd/powerplay: enable Sienna Cichlid mgpu fan boost feature

Support Sienna Cichlid mgpu fan boost enablement.

Signed-off-by: Evan Quan <evan.quan@amd.com>
Acked-by: Nirmoy Das <nirmoy.das@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>