drm/amdgpu: cleanup useless extern functions

Signed-off-by: Huang Rui <ray.huang@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/vi_dpm.h

@@ -29,8 +29,4 @@ int cz_smu_init(struct amdgpu_device *adev);
 int cz_smu_start(struct amdgpu_device *adev);
 int cz_smu_fini(struct amdgpu_device *adev);
 
-extern const struct amd_ip_funcs tonga_dpm_ip_funcs;
-extern const struct amd_ip_funcs fiji_dpm_ip_funcs;
-extern const struct amd_ip_funcs iceland_dpm_ip_funcs;
-
 #endif