drm/amd/powerplay: add DFCstate control pptable func for arct

This is the callback function that is going to be invoked
when amdgpu_dpm_set_df_cstate is called to toggle DFCstate

Signed-off-by: Hawking Zhang <Hawking.Zhang@amd.com>
Reviewed-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>