video: Move last_sync to private data

Rather than using a static variable, use the video device's private
data to remember when the last video sync was completed. This allows
each display to have its own sync and avoids using static data in SPL.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/include/video.h b/include/video.h
index 4d8df9b..4013a94 100644
--- a/include/video.h
+++ b/include/video.h
@@ -97,6 +97,7 @@
  *		the LCD is updated
  * @fg_col_idx:	Foreground color code (bit 3 = bold, bit 0-2 = color)
  * @bg_col_idx:	Background color code (bit 3 = bold, bit 0-2 = color)
+ * @last_sync:	Monotonic time of last video sync
  */
 struct video_priv {
 	/* Things set up by the driver: */
@@ -121,6 +122,7 @@
 	bool flush_dcache;
 	u8 fg_col_idx;
 	u8 bg_col_idx;
+	ulong last_sync;
 };
 
 /**