drm/amd/pp: thermal control not enabled on vega10.

regression issue.
caused by "f12f9f5e5d455edebc01"
forget to set start_thermal_controller function point.

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