overlay: writeback: Add dumpsys info

Add dumpsys information from writeback data structure.
Remove some unused fields, formatting to save space.

Change-Id: I808ce67aae16e27c3aa6d6db45983929b1386b69
diff --git a/liboverlay/overlayRotator.cpp b/liboverlay/overlayRotator.cpp
index 84a9818..7b3dda1 100644
--- a/liboverlay/overlayRotator.cpp
+++ b/liboverlay/overlayRotator.cpp
@@ -168,8 +168,8 @@
             mRot[i]->getDump(buf, len);
         }
     }
-    char str[32] = {'\0'};
-    snprintf(str, 32, "\n================\n");
+    char str[4] = {'\0'};
+    snprintf(str, 4, "\n");
     strncat(buf, str, strlen(str));
 }