drm/amd/powerplay: add function to enable thermal alert

Add function to enable thermal alerts on thermal control for smu11.

Signed-off-by: Likun Gao <Likun.Gao@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>