AMD Freesync patches for proper vblank and pageflip timestamping in VRR mode.

[Mario Kleiner]

Hi

This series implements properly working vblank and pageflip completion
timestamping for amdgpu in VRR / FreeSync mode.

Now pageflip timestamps for pageflip events always carry the
vblank timestamp of the vblank in which the flip completed,
and the vblank timestamp is as accurate as in fixed refresh
rate mode.

It was successfully tested on a DCE-8 gpu by myself, and also
lightly tested on a DCN-1 gpu by Nicholas Kazlauskas.

I want to thank Nicholas for helpful discussions, testing and
feedback on this patch series.

The series applies cleanly to current agd5f/drm-next-5.2-wip, against
which it was tested. It also applies against current amd-staging-drm-next
with a trivial fix to patch 2/4 like shown in the diff below:

Thanks,
-mario

@@ -80,2 +80,3 @@
 -      uint32_t target, target_vblank;
+       bool pflip_present = false;
 -      uint64_t last_flip_vblank;
@@ -84,3 +85,2 @@
 +      bool vrr_active = amdgpu_dm_vrr_active(acrtc_state);
-       bool pflip_present = false;