drm/amd/powerplay: use work queue to perform throttling logging

As IO operations(access to SMU internals) and possible sleep are
involved in throttling logging. Workqueue can handle them well.
Otherwise we may hit "scheduling while atomic" error.

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