Add buffer management to V4L2 wrapper.

Functions to enqueue and dequeue buffers.
Extended gralloc helper with a mass-unlock function.

Change-Id: I72c83138fd37463d314bf02b5df5befc68bc05af
diff --git a/modules/camera/3_4/V4L2Gralloc.h b/modules/camera/3_4/V4L2Gralloc.h
index a58a84d..ebec963 100644
--- a/modules/camera/3_4/V4L2Gralloc.h
+++ b/modules/camera/3_4/V4L2Gralloc.h
@@ -46,6 +46,8 @@
   // Unlock a buffer that was locked by this helper (equality determined
   // based on buffer user pointer, not the specific object).
   int unlock(const v4l2_buffer* device_buffer);
+  // Release all held locks.
+  int unlockAllBuffers();
 
 private:
   // Constructor is private to allow failing on bad input.