add set_gfx_cgpg implement

v2: check if using sw_smu (Alex)
Signed-off-by: NAaron Liu <aaron.liu@amd.com>
Reviewed-by: NHuang Rui <ray.huang@amd.com>
Reviewed-by: NEvan Quan <evan.quan@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>