drm/amd/amdgpu: finish delay works before release resources

flush/cancel delayed works before doing finalization
to avoid concurrently requests.

Signed-off-by: Jesse Zhang <zhexi.zhang@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>