drm/amd/powerplay: try to do a graceful shutdown on SW CTF

Normally this(SW CTF) should not happen. And by doing graceful
shutdown we can prevent further damage.

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