hardware: camera_common: add module open legacy device API

This adds the module API to open a camera device as lower HAL version legacy
device.

Change-Id: I6616aebc5ec0cef28f675e5dddb334dc6b5dfea9
diff --git a/modules/camera/CameraHAL.cpp b/modules/camera/CameraHAL.cpp
index b04cf0c..6f64a0d 100644
--- a/modules/camera/CameraHAL.cpp
+++ b/modules/camera/CameraHAL.cpp
@@ -184,6 +184,7 @@
     get_camera_info       : get_camera_info,
     set_callbacks         : set_callbacks,
     get_vendor_tag_ops    : get_vendor_tag_ops,
+    open_legacy           : NULL,
     reserved              : {0},
 };
 } // extern "C"