drm: Add high-precision time to vblank trace event

Store the timestamp of the current vblank in the new field 'time' of the
vblank trace event. If the timestamp is calculated by a driver that
supports high-precision vblank timing, set the field 'high-prec' to
'true'.

User space can now access actual hardware vblank times via the tracing
infrastructure. Tracing applications (such as GPUVis, see [0] for
related discussion), can use the newly added information to conduct a
more accurate analysis of display timing.

v2 Fix author name (missing last name)

[0] mikesart/gpuvis#30

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Heinrich Fink <heinrich.fink@daqri.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20190902142412.27846-2-heinrich.fink@daqri.com

drivers/gpu/drm/drm_vblank.c

@@ -1748,7 +1748,8 @@ static void drm_handle_vblank_events(struct drm_device *dev, unsigned int pipe)
 	}
 
 #ifdef __linux__
-	trace_drm_vblank_event(pipe, seq);
+	trace_drm_vblank_event(pipe, seq, now,
+			dev->driver->get_vblank_timestamp != NULL);
 #endif
 }