drm/amdgpu: apply dm_pp_notify_wm_clock_changes() for Polaris only

Will expand it to other ASICs after verified.

Signed-off-by: Evan Quan <evan.quan@amd.com>
Acked-and-tested-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>