drm/amd/display: Leave DCN config guard around fpu header

See
https://lists.freedesktop.org/archives/dri-devel/2017-August/149938.html



Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Reviewed-by: Jordan Lazare <Jordan.Lazare@amd.com>
Acked-by: Harry Wentland <Harry.Wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>