Some HW ip blocks need call SMU to enter/leave power gate state.
So export common set_powergating_by_smu interface.

1. keep consistent with set_clockgating_by_smu
2. scales easily to powergate other ip(gfx) if necessary
Reviewed-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Rex Zhu <Rex.Zhu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>