drm/amdgpu/powerplay: enable thermal interrupt task in eventmgr.

Add thermal handling to the event manager.

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