User can use "pp_dpm_fclk" to retrieve and adjust fclock power
levels.

V2: expose this interface for Vega20 and later ASICs only
Signed-off-by: Evan Quan <evan.quan@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>