drm/amd/powerplay: refine code for thermal control in powerplay

add function point start_thermal_controller in hwmgr,
delete thermal function table and related functions

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>