drm/amd/display: Use the right surface for flip and FreeSync

drm/amd/display: Use the right surface for flip and FreeSync

[Why]
We were always passing the first surface on the stream status for
flip updates when we should be using the surface associated with
the plane.

[How]
Use the dc_plane_state from the plane that's being updated.

FreeSync should also only keep track of updates from the primary
plane, so the check needed to be updated.

The acrtc->stream state doesn't need to be checked for NULL before
updating FreeSync either since there needs to be a stream to be
inside this function as a prerequisite.

Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: David Francis <David.Francis@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>