Camera3: Add support for pre capture cancel

Added enumeration for pre capture cancel

Change-Id: Ib7050f400a28d4c9307c73c9c1c70eb7bc3a66a9
diff --git a/QCamera2/stack/common/cam_types.h b/QCamera2/stack/common/cam_types.h
index 04a42b7..793de71 100644
--- a/QCamera2/stack/common/cam_types.h
+++ b/QCamera2/stack/common/cam_types.h
@@ -696,7 +696,8 @@
 
 typedef enum {
     CAM_AEC_TRIGGER_IDLE,
-    CAM_AEC_TRIGGER_START
+    CAM_AEC_TRIGGER_START,
+    CAM_AEC_TRIGGER_CANCEL
 } cam_aec_trigger_type_t;
 
 typedef enum {