drm/amd/powerplay: add new function point in hwmgr_func for CG/PG.

Add callbacks interface for clock and powergating.

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