New df helpers for 3.6.

v2: switch to using df 3.6 headers (Alex)
Acked-by: NChristian König <christian.koenig@amd.com>
Signed-off-by: NFeifei Xu <Feifei.Xu@amd.com>
Reviewed-by: NHawking Zhang <Hawking.Zhang@amd.com>
Reviewed-by: NHuang Rui <ray.huang@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>