msm_fb: display: allocate mdp writeback memory

The writeback buffer is already reserved on the board side. This
allocation separate writeback buffer from framebuffer.

Change-Id: I312be3e0dfcf4c5b611cd06cd68d2baae7e2add8
Signed-off-by: Huaibin Yang <huaibiny@codeaurora.org>
diff --git a/drivers/video/msm/msm_fb.h b/drivers/video/msm/msm_fb.h
index de2734d..9ee8972 100644
--- a/drivers/video/msm/msm_fb.h
+++ b/drivers/video/msm/msm_fb.h
@@ -166,6 +166,8 @@
 	struct completion msmfb_update_notify;
 	struct completion msmfb_no_update_notify;
 	u32 ov_start, ov_end;
+	void *writeback_overlay0_phys;
+	void *writeback_overlay1_phys;
 	struct mutex writeback_mutex;
 	struct mutex unregister_mutex;
 	struct list_head writeback_busy_queue;