libcopybit: Add Async mode support for C2D

- flush_get_fence API to copybit.h - which is async,
  which returns the fenceFD
- flush_get_fence calls C2dflush and c2dCreateFenceFD
  signals the c2d_wait_thread which waits for
  transcation to finish and cleanup resources

Change-Id: I98d5e08ea1cbce9732970c68c1e47b6f396249ce
diff --git a/libcopybit/copybit.h b/libcopybit/copybit.h
index 5adc433..d57b84d 100644
--- a/libcopybit/copybit.h
+++ b/libcopybit/copybit.h
@@ -240,6 +240,16 @@
     */
   int (*finish)(struct copybit_device_t *dev);
 
+  /**
+    * Trigger the copybit draw operation(async).
+    *
+    * @param dev from open
+    *
+    * @param fd - gets the fencefd
+    *
+    * @return 0 if successful
+    */
+  int (*flush_get_fence)(struct copybit_device_t *dev, int* fd);
 };