drm/amd/powerplay: not free hwmgr/smumgr in asic private functions.

struct smumgr/hwmgr will be freed on amd_powerplay_destory

and if we free them in one of asic private functions, other private
date may not be freed. for example: power state and power table
in hwmgr.

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